Adsorption
The term adsorption implies the presence of excess concentration of any particular component in one of the three phases of matter (known as adsorbate) at the surface of liquid or solid phase (known as adsorbent) as compared to that present in the bulk of the material.
Colloids
Colloids or sols are the substances whose sizes lie in between the solutes present in a true solution (e.g., salt, sugar) and the solutes present in suspension (e.g., sand).
The diameters of colloidal particles may range from 1 to 100 nm. The particles in colloidal state do not settle down on standing, are not visible and they can pass through a filter paper. However, they do not pass through a perchment paper or animal membrane.
Emulsion
Emulsion is a liquid dispersed in a liquid.
Wednesday, February 20, 2008
Glossary - Isomerism - for IIT JEE
Isomerism
The existence of two or more compounds with same molecular formula but different properties (physical, chemical or both) is known as isomerism; and the compounds themselves are called isomers.
Isomerism types:
i) Chain, nuclear or skeleton isomerism
This type of isomerism is due to the difference in the nature of the carbon chain (i.e. straight or branched) which forms the nucleus of the molecule,
ii) Position isomerism
It is due to the difference in the position of the substituent atom or group or an unsaturated linkage in the same carbon chain.
iii) Functional isomerism
This type of isomerism is due to difference in the nature of functional group present in the isomers,
iv) Metamerism
It is due to the difference in nature of alkyl groups attached to the same functional group. This type of isomerism is shown by compounds of the same homologous series.
v) Tautomerism
Tautomerism may be defined as the phenomenon in which a single compound exists in two readily interconvertible structures that differ markedly in the relative position of at least one atomic nucleus, generally hydrogen. The two different structures are known as tautomers of each other.
Stereo isomerism
When isomers have the same structural formula but differ in relative arrangement of atoms or groups in space within the molecule, these are known as stereoisomers and the phenomenon as stereoisomerism. The spatial arrangement of atoms or groups is also referred to as configuration of the molecule and thus we can say that the stereoisomers have the same structural formula but different configuration. Stereoisomerism is of two types.
(i) Geometrical isomerism
The isomers which possess the same structural formula but differ in the spatial arrangement of the groups around the double bond are known as geometrical isomers and the phenomenon is known as geometrical isomerism.
ii) Optical isomerism
This type of isomerism arises from different arrangements of atoms or groups in three dimensional space resulting in two isomers which are mirror image of each other. Optical isomers contain an asymmetric (chiral) carbon atom ( a carbon atom attached to four different atoms or groups) in their molecules.
The existence of two or more compounds with same molecular formula but different properties (physical, chemical or both) is known as isomerism; and the compounds themselves are called isomers.
Isomerism types:
i) Chain, nuclear or skeleton isomerism
This type of isomerism is due to the difference in the nature of the carbon chain (i.e. straight or branched) which forms the nucleus of the molecule,
ii) Position isomerism
It is due to the difference in the position of the substituent atom or group or an unsaturated linkage in the same carbon chain.
iii) Functional isomerism
This type of isomerism is due to difference in the nature of functional group present in the isomers,
iv) Metamerism
It is due to the difference in nature of alkyl groups attached to the same functional group. This type of isomerism is shown by compounds of the same homologous series.
v) Tautomerism
Tautomerism may be defined as the phenomenon in which a single compound exists in two readily interconvertible structures that differ markedly in the relative position of at least one atomic nucleus, generally hydrogen. The two different structures are known as tautomers of each other.
Stereo isomerism
When isomers have the same structural formula but differ in relative arrangement of atoms or groups in space within the molecule, these are known as stereoisomers and the phenomenon as stereoisomerism. The spatial arrangement of atoms or groups is also referred to as configuration of the molecule and thus we can say that the stereoisomers have the same structural formula but different configuration. Stereoisomerism is of two types.
(i) Geometrical isomerism
The isomers which possess the same structural formula but differ in the spatial arrangement of the groups around the double bond are known as geometrical isomers and the phenomenon is known as geometrical isomerism.
ii) Optical isomerism
This type of isomerism arises from different arrangements of atoms or groups in three dimensional space resulting in two isomers which are mirror image of each other. Optical isomers contain an asymmetric (chiral) carbon atom ( a carbon atom attached to four different atoms or groups) in their molecules.
Glossary - Inductance - Resonance - for IIT JEE
Hyperconjugation
When a H-C bond is attached to a double or triple bond in an unsaturated hydrocarbon, the sigma electrons of the H-C bond interact or enter into conjugation with the unsaturated system.
The interactions with between electrons of π systems (multiple bonds) and the adjacent sigma bonds (single H-C bonds) of the substituent groups in organic compounds is called hyperconjugation.
According to this concept, if an alkyl group carrying at least one hydrogen atom is attached to a unsaturated carbon atom, it releases electrons of carbon-hydrogen single bond towards the multiple bonds.
Hyperconjugation effect is similar to resonance effect.
When a H-C bond is attached to a double or triple bond in an unsaturated hydrocarbon, the sigma electrons of the H-C bond interact or enter into conjugation with the unsaturated system.
The interactions with between electrons of π systems (multiple bonds) and the adjacent sigma bonds (single H-C bonds) of the substituent groups in organic compounds is called hyperconjugation.
According to this concept, if an alkyl group carrying at least one hydrogen atom is attached to a unsaturated carbon atom, it releases electrons of carbon-hydrogen single bond towards the multiple bonds.
Hyperconjugation effect is similar to resonance effect.
Glossary - Alkyl and Aryl Halides for IIT JEE
Allylic, Akyl, arylic, benzylic and vinylic carbon, Hydrogen, halide
allylic carbon: a carbon adjacent to a C=C double bond
allylic hydrogen: a hydrogen on an allylic carbon
an allylic C-H bond is weaker than a vinylic C-H bond
Alkyl halide: a compound containing a halogen atom covalently bonded to an sp3 hybridized carbon atom.
Given the symbol R-X
If it is bonded to a benzene ring, it is called an aryl halide, given the symbol Ar-X
carbon next to a benzene ring is called benzylic carbon and the hydrogens on benzylic carbon are called benzylic hydrogens
If the halogen is bonded to an sp² hybridized carbon, it is a called a vinylic halide
Allylic and benzylic positions are more reactive than other positions in free radical halogenations
allylic carbon: a carbon adjacent to a C=C double bond
allylic hydrogen: a hydrogen on an allylic carbon
an allylic C-H bond is weaker than a vinylic C-H bond
Alkyl halide: a compound containing a halogen atom covalently bonded to an sp3 hybridized carbon atom.
Given the symbol R-X
If it is bonded to a benzene ring, it is called an aryl halide, given the symbol Ar-X
carbon next to a benzene ring is called benzylic carbon and the hydrogens on benzylic carbon are called benzylic hydrogens
If the halogen is bonded to an sp² hybridized carbon, it is a called a vinylic halide
Allylic and benzylic positions are more reactive than other positions in free radical halogenations
Glossary - Aldehydes and Ketones - for IIT JEE
Aldehydes
Aldehydes contain carbonyl group C=O as functional group and the carbonyl atom carries at least one H atom.
Cannizzaro reaction
Aldehydes which do not have α-hydrogen atom react with concentrated sodium hydroxide (NaOH) or potassium hydroxide (KOH) in such a way that one molecule get oxidized to acid and the second molecule gets reduced to alcohol.
Note two molecules of aldehyde participates in the reaction.
This self oxidation-reduction under the influence of a base is known as the Cannizzaro's reaction.
Ketones
In ketones, also carbonyl group C=O is the functional group. But the carbonyl carbon does not contain any H atoms, but it is attached to two alkyl or aryl groups.
Cannizzaro reaction
Aldehydes which do not have α-hydrogen atom react with concentrated sodium hydroxide (NaOH) or potassium hydroxide (KOH) in such a way that one molecule get oxidized to acid and the second molecule gets reduced to alcohol.
Note two molecules of aldehyde participates in the reaction.
This self oxidation-reduction under the influence of a base is known as the Cannizzaro's reaction.
Aldehydes contain carbonyl group C=O as functional group and the carbonyl atom carries at least one H atom.
Cannizzaro reaction
Aldehydes which do not have α-hydrogen atom react with concentrated sodium hydroxide (NaOH) or potassium hydroxide (KOH) in such a way that one molecule get oxidized to acid and the second molecule gets reduced to alcohol.
Note two molecules of aldehyde participates in the reaction.
This self oxidation-reduction under the influence of a base is known as the Cannizzaro's reaction.
Ketones
In ketones, also carbonyl group C=O is the functional group. But the carbonyl carbon does not contain any H atoms, but it is attached to two alkyl or aryl groups.
Cannizzaro reaction
Aldehydes which do not have α-hydrogen atom react with concentrated sodium hydroxide (NaOH) or potassium hydroxide (KOH) in such a way that one molecule get oxidized to acid and the second molecule gets reduced to alcohol.
Note two molecules of aldehyde participates in the reaction.
This self oxidation-reduction under the influence of a base is known as the Cannizzaro's reaction.
Glossary - Carboxylic Acids - for IIT JEE
Carboxylic acids
Carboxylic acids are the compound containing carboxyl group in their molecules.
-C with a double bond with oxygen and single bond with OH
Esters
Esters are compounds which are formed when the hydroxy hydrogen atom in oxygen acids is replaced by an alkyl group. The acid may be organic or inorganic.
Esters of organic acid:
These are compounds formed by replacing the hydrogen atom of the carboxyl group by an alkyl group.
In -COOH of carboxylic acids H is replaced an alkyl group.
It may be represented as R-COO-R'.
Carboxylic acids are the compound containing carboxyl group in their molecules.
-C with a double bond with oxygen and single bond with OH
Esters
Esters are compounds which are formed when the hydroxy hydrogen atom in oxygen acids is replaced by an alkyl group. The acid may be organic or inorganic.
Esters of organic acid:
These are compounds formed by replacing the hydrogen atom of the carboxyl group by an alkyl group.
In -COOH of carboxylic acids H is replaced an alkyl group.
It may be represented as R-COO-R'.
Glossary -Amines -for IIT JEE
AMIDES
"amide" is for the CONH2 or CONR2(more general) bond system at the end of the carbon chain
PRIMARY ACID AMIDES
The primary suffix name for an aliphatic acid amide is based on the "longest carbon chain name (without e)" + "amide" for the CONH2 bond system at the end of the carbon chain e.g. methanamide, ethanamide etc. There are two hydrogens on the N of the amide group.
SECONDARY ACID AMIDES
These have one hydrogen and one alkyl or aryl group on the N of the amide group.
TERTIARY ACID AMIDES
These have two alkyl or aryl groups attached to the N of the amide group.
POLYAMIDES and POLYPEPTIDES are secondary amides formed in a condensation reaction between a carboxylic acid and an amine. Water is eliminated between the two 'monomers' to give the secondary, polyamide (polymer) or polypeptide ( in proteins) linkage
AminesAmines are regarded as derivatives of ammonia in which one, two or all three hydrogen atoms are replaced by alkyl or aryl group.
Carbylamine reaction
The treatment of a primary amine with chloroform and alcoholic potash produces carbylamine (isocyanide) which has most offensive smell. This reaction is not exhibited by secondary and tertiary amines.
"amide" is for the CONH2 or CONR2(more general) bond system at the end of the carbon chain
PRIMARY ACID AMIDES
The primary suffix name for an aliphatic acid amide is based on the "longest carbon chain name (without e)" + "amide" for the CONH2 bond system at the end of the carbon chain e.g. methanamide, ethanamide etc. There are two hydrogens on the N of the amide group.
SECONDARY ACID AMIDES
These have one hydrogen and one alkyl or aryl group on the N of the amide group.
TERTIARY ACID AMIDES
These have two alkyl or aryl groups attached to the N of the amide group.
POLYAMIDES and POLYPEPTIDES are secondary amides formed in a condensation reaction between a carboxylic acid and an amine. Water is eliminated between the two 'monomers' to give the secondary, polyamide (polymer) or polypeptide ( in proteins) linkage
AminesAmines are regarded as derivatives of ammonia in which one, two or all three hydrogen atoms are replaced by alkyl or aryl group.
Carbylamine reaction
The treatment of a primary amine with chloroform and alcoholic potash produces carbylamine (isocyanide) which has most offensive smell. This reaction is not exhibited by secondary and tertiary amines.
Sunday, February 10, 2008
75 Suggestions to improve memory - IIT JEE Candidates
Be In the Moment
1.Focus on learning.
You can't remember something if you've never learned it, so focus on learning.
2. You don't need to enroll in a college to learn - you can learn something from educational television programs, from online courses, from books, or from other individuals.
3. It only takes about eight seconds to process data through your hippocampus into the appropriate memory center, so it doesn't take long to absorb information.
4. You need to pay attention to your environment so that you can encode this information into your brain.
5.focus on the present while learning:
To learn how to stay in the moment, don't focus on the past or worry about the future while you're learning.
6. Concentrate: Don't multitask, as you create a "brain drain" when you focus on more than one activity.
Create a Learning Environment
7. Note the environments that make it easier for you to concentrate and try to replicate those environments for learning. You may be accustomed to background noise (like traffic), or you may need complete silence, depending upon the task and your learning habits.
8. To that end, it would help if you understood your learning style. Once you understand what works for you, you can create an environment that stimulates your strengths.
9. Create a learning environment at home. You can learn how to expand on those environments in articles written by professionals for teachers and their students.
10. If you plan to learn online, know what you need to own before you can begin this task successfully.
11. If you are a visual learner, make sure you have tools to create visuals that will help you retain information.
12. If you're an auditory learner, purchase a tape recorder so that you can use it to repeat instructions or information.
Use All Your Senses
13. If you're learning something, involve as many senses as possible to help retain the experience. read-talk(read aloud or pronounce internally so that your ear can hear)-write
14. Drawing and writing includes the use of motor skills that help you to remember information as you stimulate motor pathways.
15. If you utilize these motor skills in a task, don't try something new for a few days. Instead, repeat some of the exercises listed immediately below a few times during the first week so that they become ingrained with your learning habits.
16. For instance, if you lack charts and diagrams for your reading materials, create them yourself so that you can add sight to sound to help retain information.
17. Take notes on index cards or in a notebook as you listen to a lecture or a similar presentation so that you can help retain information.
18. Sound includes talking to yourself - although this action may not be appropriate during a lecture, you can read your notes aloud when you're alone.
19.Explain to others what you have learned - Talk with another person about the information you've gathered. This action will incorporate more than one sense and it will help you to categorize information as well.
20. If you're studying information that includes models (like a car engine), touch various parts (as long as it's safe to touch them) to help memorize those parts.
21. Attach your ideas to an inert object for your learning process. For instance, connect the introduction of a speech to the entrance of the house, move on to the next room to connect the introduction to the next idea, and so on throughout a building.
22. Along the same lines, you can attach steps within a learning process to actual stairways or to stairs that you draw.
23. Although taste and smell both evoke strong memories, they aren't very convenient for organizing or holding information in your mind. But, you can try to remember a difficult task by sucking on a mint or by eating a fruit. The taste and smell may stimulate your thought processes when you try to remember the information that you learned (like the memory of chalk dust in a classroom).
Use Mnemonic Devices
24. Mnemonic (the initial "m" is silent) devices can provide clues to help you remember things. For instance, you can use visual images to memorize names, places, and events. If you wanted to remember Tom's name, think of a tom cat and connect that person to that image. Or, use something more obvious, like Queen Victoria for Victoria. Just place an imaginary crown on Victoria's head and you might remember that person's name the next time you meet them.
25. Use positive or amusing images rather than unpleasant ones, as them brain often blocks out distasteful memories.
26. If you make the images colorful and three-dimensional, they'll be easier to remember.
27. "Every Good Boy Does Fine" is a sentence that many musicians use to remember the lines in a treble staff (E, G, B, D, and F). Medical students use silly sentences to remember anatomical features. Try this tool when you need to memorize a sequence of difficult words or a series like the biological taxonomy (Kingdom, Phylum, Class, Order, Family, Genus, Species): "Kids Played Cards On Furry Gray Skins."
28. "FACE" is the other tool that musicians use to remember the spaces between the lines on the treble staff (F, A, C, and E). This is called an acronym, or using the first letter of a word to create a new word. Other examples include SCUBA (self-contained underwater breathing apparatus), ANZAC (Australian and New Zealand Army Corps), and HOMES (Huron, Ontario, Michigan, Erie, and Superior - the great lakes).
29. Use alliteration to help memorize certain data. "She sells seashells by the seashore" is one example of alliteration. You can group certain words within a list to create a silly alliterative sentence that will be easy to remember.
30. With that said, use alliteration to remember peoples' names. When you meet a large man named Stan, you could call him "Substantial Stan" (but not to his face!) so you can remember his name. If he loses weight, however, you might be in trouble.
31. Rhymes also are useful for memorization. You might remember this one: "In fourteen hundred ninety-two, Columbus sailed the ocean blue." If you need to remember that your business partner is allergic to peanuts, you could make up a rhyme like this: "I'll feel like a klutz if I offer him nuts."
32. “Chunk” information, or arrange a long list into smaller units or categories that will be easier to remember. Your Social Security number, for instance, is easier to remember as three "chunks" of three, two, and four numbers rather than a long string of numbers. Phone numbers, credit card numbers, passwords, and other long sequences can be memorized in chunks as well.
33. When you relate a speech to a house (see #21), you're using what is called a "Method of loci." For instance, if you're learning certain body parts, you can place one in the fridge, one in the oven, and another in the bathroom cabinet. Or, use your route to work to associate learning with various landmarks.
34. Connect new data to information you already know. Remember you X class knowledge and add new information that you are now learning. It will help you to remember better.
Organize
35. Disorganized people report more memory problems than those individuals who are accustomed to organization. This ability to organize is external as well as internal...External organization can free your brain up for more creative endeavors. Internal organization requires a less stressful lifestyle.
36. Write things down, but write them down in appropriate places. For instance, write addresses in address books, and write grocery lists in a special notebook that you've designated for that list. Accordingly, use specific places in the house for certain items. For instance, if you hang the keys on a hook by the door when you enter, you won't need to sap your time or brain power to find those keys.
37. Lists are great for handling stress - even if the list is a long one, it will be rewarding to cross items off as you complete them.
38. Learn how to prioritize. Get the small things done first so that your list is shortened quickly. For instance, as you go through your email, reply to the ones that need a response immediately so that they don't pile up. In that vein, you really don't need to remember all the names of the individuals you met at that business meeting. Focus on the less than ten names of individuals who you want to meet again.
39. Use online or paper calendars to remember important dates. This will help you to be more social, on time, and employed. Plus, you can free up your mind for more creative endeavors.
40. Use both words and pictures to help retain information about such things as meeting dates and places.
41. Break detailed ideas down into simple thoughts that you can convey to someone else (or to yourself). This effort is similar to 'chunking' (see #32), and it will help you to remember complex ideas.
42. Similarly, if you understand basic concepts, this memory will help you to retrieve isolated details about that concept.
43. When you can't write something down, visualize those ideas as being compartmentalized in your brain, much like you would file information away into a filing cabinet. But, be careful and try to make those lists, as an overstuffed file system in your brain can contribute to memory losses.
44. Keep a pad, pencil and small flashlight by your bed to write down ideas that you have at night. If you forget these tools, just move something out of place so that you'll remember that idea in the morning (just throw a tissue or book on the floor so you see it in the morning - those items will trigger memories of the previous evening).
45. Increase your scholarly productivity with tools that will help you stay organized online.
Overlearn very important idea
46. Spend some time with new material a few hours after you've been introduced to it. Read the material in the night after the class. Review notes and try to consolidate the notes into a broad concept or idea.
47. Review notes and other information at intervals throughout the next few days. This is called "Spaced Rehearsal" or "Spaced Repetition," and it's a more effective method for learning than cramming. Review each lesson two or more times in the next seven days.
48. Review material until it becomes second nature. The best way to accomplish this task is to discuss material with another person.
49. When you use overlearning, you improve recall speed.
Retain a Positive Attitude
50. Take interest in learning. If you don't want to learn something, chances are you won't learn it.
51. Tell yourself that you want to learn and that you can learn and remember the information at hand.
52. Don't blame your brain. If you constantly tell yourself and others that you have a bad memory, this action actually hampers the ability of your brain to remember.
53. A positive outlook and positive mental feedback sets up an expectation for success.
Exercise Regularly
54. Exercise increases oxygen to the brain, and oxygen is important for brain function.
55. Physical exercise reduces the risk for disorders that lead to memory loss, such as diabetes and cardiovascular disease.
56. A mix of programs that involve both aerobic exercise and strength training are of greatest benefit, with exercise sessions lasting at least 30 minutes.
57. Exercise may enhance the effects of helpful brain chemicals and protect brain cells, and it may increase the flow of blood to the hippocampus (see #3), enabling it to function better.
58. The hippocampus is especially vulnerable to age-related deterioration that can affect how well you retain information, so it's important to maintain an exercise routine as you age.
59. Exercise helps to control blood sugar levels, and a recent study has found that those with impaired glucose tolerance and/or chronic stress tend to have a smaller hippocampus. Since the hippocampus is vital to memory retention, this is not a good thing.
60. Exercise may increase self-confidence, and may reduce anxiety and depression and help you to retain a more positive attitude about life.
61. Even if you are too busy with studies, take a break to walk around the block. The exercise will help you stay connected and stimulated.
62. Walking is not strenuous (unless you power walk), so your leg muscles don't take up extra oxygen and glucose like they do during other forms of exercise. If you find yourself stressed, take a few minutes to oxygenate your brain with a leisurely walk.
63. Movement and exercise increase breathing and heart rate so that more blood flows to the brain, enhancing energy production and waste removal. As you increase your strength, you also increase your capacity to remember.
64. Physical exercise can protect your brain and its mental processes
Manage stress
65. Cortisol, the stress hormone secreted under stress by the human adrenal gland, near the kidneys, can damage the hippocampus if stress is unrelieved.
66. Stress can produce an enzyme called, "protein kinase C," which impairs the short-term memory and other functions in the prefrontal cortex, the executive-decision part of the brain. In other words, stress can make it difficult to remember and to concentrate.
67. Physical exercise can help to relieve stress. Even a simple walk can help to clear the mind.
68. Jokes, soothing music, and even a short nap can help to break the stress.
69. On the other hand, arousing, exciting, momentous occasions, including stressful ones, get filed away very readily. If you can remember your first job, 9/11, or when Kennedy was shot, these examples prove that some stressful occasions can create vivid memories.
70. It has been discovered that people who are more prone to chronic distress are more likely to develop Alzheimer’s disease than their more carefree counterparts.
Other Good habits
71. A good night's sleep is necessary for memory consolidation. lakc of sleep disorders can leave you tired and unable to concentrate during the day.
72. Smoking constricts arteries that deliver oxygen to the brain. Tests have proven this memory loss in adolescents who smoke.
73. Relaxation through meditation, tai chi, yoga, or other techniques that slow respiration, slow metabolism, and release muscle tension can make a huge difference in your overall health and stress levels. Invest about ten to fifteen minutes per day with these techniques.
74. Investigate biofeedback programs or games that provide real-time information and tracking. These tools can help you learn effective techniques for reducing stress.
75. Staying properly hydrated can do more for your body and mind than eating, at times. Drink your recommended 8-10 glasses day.
http://oedb.org/library/features/the-memory-toolbox
http://www.academictips.org/memory/index.html
http://www.helpguide.org/life/improving_memory.htm
1.Focus on learning.
You can't remember something if you've never learned it, so focus on learning.
2. You don't need to enroll in a college to learn - you can learn something from educational television programs, from online courses, from books, or from other individuals.
3. It only takes about eight seconds to process data through your hippocampus into the appropriate memory center, so it doesn't take long to absorb information.
4. You need to pay attention to your environment so that you can encode this information into your brain.
5.focus on the present while learning:
To learn how to stay in the moment, don't focus on the past or worry about the future while you're learning.
6. Concentrate: Don't multitask, as you create a "brain drain" when you focus on more than one activity.
Create a Learning Environment
7. Note the environments that make it easier for you to concentrate and try to replicate those environments for learning. You may be accustomed to background noise (like traffic), or you may need complete silence, depending upon the task and your learning habits.
8. To that end, it would help if you understood your learning style. Once you understand what works for you, you can create an environment that stimulates your strengths.
9. Create a learning environment at home. You can learn how to expand on those environments in articles written by professionals for teachers and their students.
10. If you plan to learn online, know what you need to own before you can begin this task successfully.
11. If you are a visual learner, make sure you have tools to create visuals that will help you retain information.
12. If you're an auditory learner, purchase a tape recorder so that you can use it to repeat instructions or information.
Use All Your Senses
13. If you're learning something, involve as many senses as possible to help retain the experience. read-talk(read aloud or pronounce internally so that your ear can hear)-write
14. Drawing and writing includes the use of motor skills that help you to remember information as you stimulate motor pathways.
15. If you utilize these motor skills in a task, don't try something new for a few days. Instead, repeat some of the exercises listed immediately below a few times during the first week so that they become ingrained with your learning habits.
16. For instance, if you lack charts and diagrams for your reading materials, create them yourself so that you can add sight to sound to help retain information.
17. Take notes on index cards or in a notebook as you listen to a lecture or a similar presentation so that you can help retain information.
18. Sound includes talking to yourself - although this action may not be appropriate during a lecture, you can read your notes aloud when you're alone.
19.Explain to others what you have learned - Talk with another person about the information you've gathered. This action will incorporate more than one sense and it will help you to categorize information as well.
20. If you're studying information that includes models (like a car engine), touch various parts (as long as it's safe to touch them) to help memorize those parts.
21. Attach your ideas to an inert object for your learning process. For instance, connect the introduction of a speech to the entrance of the house, move on to the next room to connect the introduction to the next idea, and so on throughout a building.
22. Along the same lines, you can attach steps within a learning process to actual stairways or to stairs that you draw.
23. Although taste and smell both evoke strong memories, they aren't very convenient for organizing or holding information in your mind. But, you can try to remember a difficult task by sucking on a mint or by eating a fruit. The taste and smell may stimulate your thought processes when you try to remember the information that you learned (like the memory of chalk dust in a classroom).
Use Mnemonic Devices
24. Mnemonic (the initial "m" is silent) devices can provide clues to help you remember things. For instance, you can use visual images to memorize names, places, and events. If you wanted to remember Tom's name, think of a tom cat and connect that person to that image. Or, use something more obvious, like Queen Victoria for Victoria. Just place an imaginary crown on Victoria's head and you might remember that person's name the next time you meet them.
25. Use positive or amusing images rather than unpleasant ones, as them brain often blocks out distasteful memories.
26. If you make the images colorful and three-dimensional, they'll be easier to remember.
27. "Every Good Boy Does Fine" is a sentence that many musicians use to remember the lines in a treble staff (E, G, B, D, and F). Medical students use silly sentences to remember anatomical features. Try this tool when you need to memorize a sequence of difficult words or a series like the biological taxonomy (Kingdom, Phylum, Class, Order, Family, Genus, Species): "Kids Played Cards On Furry Gray Skins."
28. "FACE" is the other tool that musicians use to remember the spaces between the lines on the treble staff (F, A, C, and E). This is called an acronym, or using the first letter of a word to create a new word. Other examples include SCUBA (self-contained underwater breathing apparatus), ANZAC (Australian and New Zealand Army Corps), and HOMES (Huron, Ontario, Michigan, Erie, and Superior - the great lakes).
29. Use alliteration to help memorize certain data. "She sells seashells by the seashore" is one example of alliteration. You can group certain words within a list to create a silly alliterative sentence that will be easy to remember.
30. With that said, use alliteration to remember peoples' names. When you meet a large man named Stan, you could call him "Substantial Stan" (but not to his face!) so you can remember his name. If he loses weight, however, you might be in trouble.
31. Rhymes also are useful for memorization. You might remember this one: "In fourteen hundred ninety-two, Columbus sailed the ocean blue." If you need to remember that your business partner is allergic to peanuts, you could make up a rhyme like this: "I'll feel like a klutz if I offer him nuts."
32. “Chunk” information, or arrange a long list into smaller units or categories that will be easier to remember. Your Social Security number, for instance, is easier to remember as three "chunks" of three, two, and four numbers rather than a long string of numbers. Phone numbers, credit card numbers, passwords, and other long sequences can be memorized in chunks as well.
33. When you relate a speech to a house (see #21), you're using what is called a "Method of loci." For instance, if you're learning certain body parts, you can place one in the fridge, one in the oven, and another in the bathroom cabinet. Or, use your route to work to associate learning with various landmarks.
34. Connect new data to information you already know. Remember you X class knowledge and add new information that you are now learning. It will help you to remember better.
Organize
35. Disorganized people report more memory problems than those individuals who are accustomed to organization. This ability to organize is external as well as internal...External organization can free your brain up for more creative endeavors. Internal organization requires a less stressful lifestyle.
36. Write things down, but write them down in appropriate places. For instance, write addresses in address books, and write grocery lists in a special notebook that you've designated for that list. Accordingly, use specific places in the house for certain items. For instance, if you hang the keys on a hook by the door when you enter, you won't need to sap your time or brain power to find those keys.
37. Lists are great for handling stress - even if the list is a long one, it will be rewarding to cross items off as you complete them.
38. Learn how to prioritize. Get the small things done first so that your list is shortened quickly. For instance, as you go through your email, reply to the ones that need a response immediately so that they don't pile up. In that vein, you really don't need to remember all the names of the individuals you met at that business meeting. Focus on the less than ten names of individuals who you want to meet again.
39. Use online or paper calendars to remember important dates. This will help you to be more social, on time, and employed. Plus, you can free up your mind for more creative endeavors.
40. Use both words and pictures to help retain information about such things as meeting dates and places.
41. Break detailed ideas down into simple thoughts that you can convey to someone else (or to yourself). This effort is similar to 'chunking' (see #32), and it will help you to remember complex ideas.
42. Similarly, if you understand basic concepts, this memory will help you to retrieve isolated details about that concept.
43. When you can't write something down, visualize those ideas as being compartmentalized in your brain, much like you would file information away into a filing cabinet. But, be careful and try to make those lists, as an overstuffed file system in your brain can contribute to memory losses.
44. Keep a pad, pencil and small flashlight by your bed to write down ideas that you have at night. If you forget these tools, just move something out of place so that you'll remember that idea in the morning (just throw a tissue or book on the floor so you see it in the morning - those items will trigger memories of the previous evening).
45. Increase your scholarly productivity with tools that will help you stay organized online.
Overlearn very important idea
46. Spend some time with new material a few hours after you've been introduced to it. Read the material in the night after the class. Review notes and try to consolidate the notes into a broad concept or idea.
47. Review notes and other information at intervals throughout the next few days. This is called "Spaced Rehearsal" or "Spaced Repetition," and it's a more effective method for learning than cramming. Review each lesson two or more times in the next seven days.
48. Review material until it becomes second nature. The best way to accomplish this task is to discuss material with another person.
49. When you use overlearning, you improve recall speed.
Retain a Positive Attitude
50. Take interest in learning. If you don't want to learn something, chances are you won't learn it.
51. Tell yourself that you want to learn and that you can learn and remember the information at hand.
52. Don't blame your brain. If you constantly tell yourself and others that you have a bad memory, this action actually hampers the ability of your brain to remember.
53. A positive outlook and positive mental feedback sets up an expectation for success.
Exercise Regularly
54. Exercise increases oxygen to the brain, and oxygen is important for brain function.
55. Physical exercise reduces the risk for disorders that lead to memory loss, such as diabetes and cardiovascular disease.
56. A mix of programs that involve both aerobic exercise and strength training are of greatest benefit, with exercise sessions lasting at least 30 minutes.
57. Exercise may enhance the effects of helpful brain chemicals and protect brain cells, and it may increase the flow of blood to the hippocampus (see #3), enabling it to function better.
58. The hippocampus is especially vulnerable to age-related deterioration that can affect how well you retain information, so it's important to maintain an exercise routine as you age.
59. Exercise helps to control blood sugar levels, and a recent study has found that those with impaired glucose tolerance and/or chronic stress tend to have a smaller hippocampus. Since the hippocampus is vital to memory retention, this is not a good thing.
60. Exercise may increase self-confidence, and may reduce anxiety and depression and help you to retain a more positive attitude about life.
61. Even if you are too busy with studies, take a break to walk around the block. The exercise will help you stay connected and stimulated.
62. Walking is not strenuous (unless you power walk), so your leg muscles don't take up extra oxygen and glucose like they do during other forms of exercise. If you find yourself stressed, take a few minutes to oxygenate your brain with a leisurely walk.
63. Movement and exercise increase breathing and heart rate so that more blood flows to the brain, enhancing energy production and waste removal. As you increase your strength, you also increase your capacity to remember.
64. Physical exercise can protect your brain and its mental processes
Manage stress
65. Cortisol, the stress hormone secreted under stress by the human adrenal gland, near the kidneys, can damage the hippocampus if stress is unrelieved.
66. Stress can produce an enzyme called, "protein kinase C," which impairs the short-term memory and other functions in the prefrontal cortex, the executive-decision part of the brain. In other words, stress can make it difficult to remember and to concentrate.
67. Physical exercise can help to relieve stress. Even a simple walk can help to clear the mind.
68. Jokes, soothing music, and even a short nap can help to break the stress.
69. On the other hand, arousing, exciting, momentous occasions, including stressful ones, get filed away very readily. If you can remember your first job, 9/11, or when Kennedy was shot, these examples prove that some stressful occasions can create vivid memories.
70. It has been discovered that people who are more prone to chronic distress are more likely to develop Alzheimer’s disease than their more carefree counterparts.
Other Good habits
71. A good night's sleep is necessary for memory consolidation. lakc of sleep disorders can leave you tired and unable to concentrate during the day.
72. Smoking constricts arteries that deliver oxygen to the brain. Tests have proven this memory loss in adolescents who smoke.
73. Relaxation through meditation, tai chi, yoga, or other techniques that slow respiration, slow metabolism, and release muscle tension can make a huge difference in your overall health and stress levels. Invest about ten to fifteen minutes per day with these techniques.
74. Investigate biofeedback programs or games that provide real-time information and tracking. These tools can help you learn effective techniques for reducing stress.
75. Staying properly hydrated can do more for your body and mind than eating, at times. Drink your recommended 8-10 glasses day.
http://oedb.org/library/features/the-memory-toolbox
http://www.academictips.org/memory/index.html
http://www.helpguide.org/life/improving_memory.htm
Prac-Org-Chemistry - Aldehydes and Ketones
Ch 34 Practical Organic Chemistry
Aldehydes and Ketones Core Points
Tests to distinguish aldehydes and ketones
1. LiAlH4
2. Fehlings solution
3. Alcohol in the prsence of HCl
4. Schiff's reagent
5. Tollen's reagent
Mnemonic to remember Learn FAST
1. LiAlH4 : Reduction with LiAlH4 - Aldehydes form primary alcohols. Ketones form secondary alcohols.
2. Fehlings solution: Aldehydes when heated with Fehling's solution give red precipitate of cuprous oxide (Cu2O). Ketones do not give precipitates.
3. Alcohol in the prsence of HCl: Action of Alcohol in the prsence of HCl: Aldehydes form acetals easily. Ketones do not form acetals easily.
4. Schiff's reagent; In reaction aldehydes give red precipitate. Ketones do not give precipitate.
5. Tollen's reagent: In reaction aldehydes form silver mirror. Ketones do not form silver mirror.
Distinction between some compounds
1. Formaldehyde (HCHO) and acetaldehyde (CH3CHO)
Acetaldehyde gives yellow precipitate of iodoform (CHI3) with an alkaline solution of iodine (I2 + NaOH)
Formaldehyde does not give this test
2. Acetaldehdye and Benzaldehyde
Acetaldehyde gives yellow precipitate of iodoform (CHI3) with an alkaline solution of iodine (I2 + NaOH)
Benzaldehyde does not give the precipitate
3. Acetaldehyde and acetone
Tollen's reagent: In reaction aldehydes form silver mirror
Acetone does not give this test
4. Benzaldehyde and acetophenone
Tollen's reagent:benzaldehyde give silver mirror.
acetophenone does not react
5. 2-Pentanone and 3-pentanone
Iodoform test
2-pentanone gives iodoform test.
3-pentannone does not give precipitate
6. Acetophenone and benzophenone
Iodoform test:
Acetophenone gives yellow precipitate of iodoform.
Benzophenone does not give this test.
Aldehydes and Ketones Core Points
Tests to distinguish aldehydes and ketones
1. LiAlH4
2. Fehlings solution
3. Alcohol in the prsence of HCl
4. Schiff's reagent
5. Tollen's reagent
Mnemonic to remember Learn FAST
1. LiAlH4 : Reduction with LiAlH4 - Aldehydes form primary alcohols. Ketones form secondary alcohols.
2. Fehlings solution: Aldehydes when heated with Fehling's solution give red precipitate of cuprous oxide (Cu2O). Ketones do not give precipitates.
3. Alcohol in the prsence of HCl: Action of Alcohol in the prsence of HCl: Aldehydes form acetals easily. Ketones do not form acetals easily.
4. Schiff's reagent; In reaction aldehydes give red precipitate. Ketones do not give precipitate.
5. Tollen's reagent: In reaction aldehydes form silver mirror. Ketones do not form silver mirror.
Distinction between some compounds
1. Formaldehyde (HCHO) and acetaldehyde (CH3CHO)
Acetaldehyde gives yellow precipitate of iodoform (CHI3) with an alkaline solution of iodine (I2 + NaOH)
Formaldehyde does not give this test
2. Acetaldehdye and Benzaldehyde
Acetaldehyde gives yellow precipitate of iodoform (CHI3) with an alkaline solution of iodine (I2 + NaOH)
Benzaldehyde does not give the precipitate
3. Acetaldehyde and acetone
Tollen's reagent: In reaction aldehydes form silver mirror
Acetone does not give this test
4. Benzaldehyde and acetophenone
Tollen's reagent:benzaldehyde give silver mirror.
acetophenone does not react
5. 2-Pentanone and 3-pentanone
Iodoform test
2-pentanone gives iodoform test.
3-pentannone does not give precipitate
6. Acetophenone and benzophenone
Iodoform test:
Acetophenone gives yellow precipitate of iodoform.
Benzophenone does not give this test.
Saturday, February 9, 2008
Ch.34 Practical Organic Chemistry - Carboxylic Acids
Distinguishing various compounds
1. Forming acid and acetic acid
i) Silver mirror test with Tollen's reagent: Formic acid gives this test and silver precipitate is formed when Tollen's reagent is added to formic acid.
Formic acid -- HCOOH
Tollen's reagent -- [Ag(NH3)2]OH
Acetic acid does not give this test.
ii) Reaction with mercuric chloride solution: Formic acid in reaction with mercuric chloride solution gives white precipitate.
Mercuric chloride--HgCl2
2. Acetic acid and acetone
Acetic acid CH3COOH
Acetone CH3COCH3
i) Reaction with sodium bicarbonate (NaHCO3): Acetic acid reacts with NaHCO3 to give effervescence as CO2 is evolved.
Acetone has no such reaction.
ii) Iodoform: Acetone reacts with alkaline solution of iodine to give yellow precipitate due to the formation of iodoform (CHI3).
Acetic acid does not give this test.
3. Ethanol and acetic acid
Ethanol C2H5OH
Ehtanol is an alcohol and acetic acid is a carboxylic acid
Carboxylic acid turns blue litmus red. Alcohol has no effect on litmus.
Alcohol has no reaction with sodium bicarbonate. Carboxylic acids give effervescence due to evolution of CO2.
Hence acetic acid gives effervescence with NaHCO3. Ethanol does not give.
Do the spot exercise - go to
http://iit-jee-chemistry-ps.blogspot.com/2008/02/ch34-poc-carboxylic-acids-spot-exercise.html
1. Forming acid and acetic acid
i) Silver mirror test with Tollen's reagent: Formic acid gives this test and silver precipitate is formed when Tollen's reagent is added to formic acid.
Formic acid -- HCOOH
Tollen's reagent -- [Ag(NH3)2]OH
Acetic acid does not give this test.
ii) Reaction with mercuric chloride solution: Formic acid in reaction with mercuric chloride solution gives white precipitate.
Mercuric chloride--HgCl2
2. Acetic acid and acetone
Acetic acid CH3COOH
Acetone CH3COCH3
i) Reaction with sodium bicarbonate (NaHCO3): Acetic acid reacts with NaHCO3 to give effervescence as CO2 is evolved.
Acetone has no such reaction.
ii) Iodoform: Acetone reacts with alkaline solution of iodine to give yellow precipitate due to the formation of iodoform (CHI3).
Acetic acid does not give this test.
3. Ethanol and acetic acid
Ethanol C2H5OH
Ehtanol is an alcohol and acetic acid is a carboxylic acid
Carboxylic acid turns blue litmus red. Alcohol has no effect on litmus.
Alcohol has no reaction with sodium bicarbonate. Carboxylic acids give effervescence due to evolution of CO2.
Hence acetic acid gives effervescence with NaHCO3. Ethanol does not give.
Do the spot exercise - go to
http://iit-jee-chemistry-ps.blogspot.com/2008/02/ch34-poc-carboxylic-acids-spot-exercise.html
Inert pair effect
The term inert pair effect is often used in relation to the increasing stability of oxidation states that are 2 less than the group valency for the heavier elements of groups 13, 14, 15 and 16.
There was a question in orkut community about it
There was a question in orkut community about it
Friday, February 8, 2008
IIT JEE Revision
Formation of esters
Esters are compounds which are formed when the hydroxy hydrogen atom in oxygen acids is replaced by an alkyl group. The acid may be organic or inorganic.
Esters of organic acid:
These are compounds formed by replacing the hydrogen atom of the carboxyl group by an alkyl group.
In -COOH of carboxylic acids H is replaced by an alkyl group.
It may be represented as R-COOH-R'.
Acetic acid + Ethanol ---> Ethyl acetate (Ethyl ethanoate) + water
Ethyl acetate (Ethyl ethanoate) is ester CH3COOC2H5
When a carboxylic acid is heated with an alcohol in presence of dehydrating agent like concentrated sulphuric acid , it gives an ester.
Posting done in
http://iit-jee-chemistry.blogspot.com/2008/02/formation-of-esters.html
Esters are compounds which are formed when the hydroxy hydrogen atom in oxygen acids is replaced by an alkyl group. The acid may be organic or inorganic.
Esters of organic acid:
These are compounds formed by replacing the hydrogen atom of the carboxyl group by an alkyl group.
In -COOH of carboxylic acids H is replaced by an alkyl group.
It may be represented as R-COOH-R'.
Acetic acid + Ethanol ---> Ethyl acetate (Ethyl ethanoate) + water
Ethyl acetate (Ethyl ethanoate) is ester CH3COOC2H5
When a carboxylic acid is heated with an alcohol in presence of dehydrating agent like concentrated sulphuric acid , it gives an ester.
Posting done in
http://iit-jee-chemistry.blogspot.com/2008/02/formation-of-esters.html
Tuesday, February 5, 2008
IIT JEE Revision - Ch. 25. Alcohols - Core Points
Syllabus
Alcohols:
esterification,
dehydration and oxidation,
reaction with sodium,
reaction with phosphorus halides,
reaction with ZnCl2/conc.-HCl,
conversion of alcohols into aldehydes and ketones;
---------
1. The hydroxy derivatives of aliphatic hydrocarbons are termed alcohols. They contain one or more hydroxyl (OH) groups.
Example:
Methyl Alcohol CH-3OH
Ehtyl alcohol C-2H-5OH also written as CH-3CH-2OH
Propyl alcohol C-3H-7OH also written as CH-3CH-2CH-2OH
2. Methods of Preparation of Alcohols
1. preparation from haloalkanes
2. By reduction of aldehydes, ketones and esters
3. Physical Properties:
4. Reaction with active metals - acidic character
5. Esterification
Alcohols react with monocarboxylic acids, in the presence of concentrated sulphuric acid or dry HCL gas as catalyst, to from esters. This reaction is known as esterification.
6. Dehydration
When alcohols are heated with conc. or H3PO4, at 443 K, they get dehydrated to form alkenes.
The ease of dehydration of alcohol follows the order 3>2>1 which is also the order of stability of carbocation.
7. Oxidation
The oxidation of alcohols can be carried out by a number of reagents such as acqueous, alkaline or acidified KMnO4, acidified Na2Cr2O7, nitric acid, chromic acid, etc.
8. Reaction with sodium
The cleavage in this reaction will be in the OH bond. Alcohols react with active metals to liberate hydrogen gas and form metal alkoxide.
Ethanol or Ethyl alcohol reacts with sodium to give Sodium ethoxide and hydrogen
9. Reaction with phosphorus halides
Phosphorus halides such as PCl5, PCl3, PBr3 and PI3 react with alcohols to form corresponding haloalkanes.
10. Reaction with ZnCl2/conc.-HCl
This is a reaction or test to distinguish various categories of alcohols and is termed Lucas test.
In this test, an alcohol is treated with an equimolar mixture of concentrated hydrochloric acid and anhydrous ZnCl2 (called Lucas reagent).
11. Conversion of alcohols into aldehydes and ketones
Oxidation of primary alcohol gives aldehydes.
Oxidation of secondary alcohols gives ketones.
It is difficult to oxidize tertiary alcohols.
Alcohols:
esterification,
dehydration and oxidation,
reaction with sodium,
reaction with phosphorus halides,
reaction with ZnCl2/conc.-HCl,
conversion of alcohols into aldehydes and ketones;
---------
1. The hydroxy derivatives of aliphatic hydrocarbons are termed alcohols. They contain one or more hydroxyl (OH) groups.
Example:
Methyl Alcohol CH-3OH
Ehtyl alcohol C-2H-5OH also written as CH-3CH-2OH
Propyl alcohol C-3H-7OH also written as CH-3CH-2CH-2OH
2. Methods of Preparation of Alcohols
1. preparation from haloalkanes
2. By reduction of aldehydes, ketones and esters
3. Physical Properties:
4. Reaction with active metals - acidic character
5. Esterification
Alcohols react with monocarboxylic acids, in the presence of concentrated sulphuric acid or dry HCL gas as catalyst, to from esters. This reaction is known as esterification.
6. Dehydration
When alcohols are heated with conc. or H3PO4, at 443 K, they get dehydrated to form alkenes.
The ease of dehydration of alcohol follows the order 3>2>1 which is also the order of stability of carbocation.
7. Oxidation
The oxidation of alcohols can be carried out by a number of reagents such as acqueous, alkaline or acidified KMnO4, acidified Na2Cr2O7, nitric acid, chromic acid, etc.
8. Reaction with sodium
The cleavage in this reaction will be in the OH bond. Alcohols react with active metals to liberate hydrogen gas and form metal alkoxide.
Ethanol or Ethyl alcohol reacts with sodium to give Sodium ethoxide and hydrogen
9. Reaction with phosphorus halides
Phosphorus halides such as PCl5, PCl3, PBr3 and PI3 react with alcohols to form corresponding haloalkanes.
10. Reaction with ZnCl2/conc.-HCl
This is a reaction or test to distinguish various categories of alcohols and is termed Lucas test.
In this test, an alcohol is treated with an equimolar mixture of concentrated hydrochloric acid and anhydrous ZnCl2 (called Lucas reagent).
11. Conversion of alcohols into aldehydes and ketones
Oxidation of primary alcohol gives aldehydes.
Oxidation of secondary alcohols gives ketones.
It is difficult to oxidize tertiary alcohols.
Alcohols - Introduction, Nomenclature
The hydroxy derivatives of aliphatic hydrocarbons are termed alcohols. They contain one or more hydroxyl (OH) groups.
Example:
Methyl Alcohol CH-3OH
Ehtyl alcohol C-2H-5OH also written as CH-3CH-2OH
Propyl alcohol C-3H-7OH also written as CH-3CH-2CH-2OH
They are classified according to the number of hydroxyl groups in the molecule.
i. Monohydric alcohol contains one -OH group.
ii. A dihydric alcohol contains two -OH groups in the molecule
ex. ethylene glycol
CH2OH
|
CH2OH
iii. A trihydric alcohol contains three -OH groups in its molecules
ex.glycerol
CH2OH
|
CH2OH
|
CH2OH
Monohydric alcohols are represented by the general formula R-OH or CnH2n+1OH.
Monohydric alcohols are further classified according to the carbon atom to which the hydroxyl group is attached.
1. Primary alcohols: -OH group is attached to primary carbon atom. They contain the group -CH2OH
eg.: CH3CH2OH, CH3CH2CH2OH
2. Secondry alcohol: -OH group is attached to a secondary carbon atom. It contains a divalent >CHOH group.
Ex. iso-propyl alcohol
3. Tertiary alcohol: -Oh group is attached to tertiary carbon atom. C-OH group is present
Alcohols – Nomenclature
Common system
Alcohols are named as alkyl alcohols. The alkyl group attached to the –OH group is named and the word alcohol is added to it.
Ex: Methyl alcohol
IUPAC nomenclature system
‘e’ in the parent chain is replaced by ‘ol’
Ex: Methanol
Rules follow for arriving at the names of alcohols
1. The longest continuous chain containing the carbon bonded to the OH group is selected as the parent chain.
2. The carbon atoms in the chain are numbered in such a way that the carbon atom carrying the hydroxyl group gets the lowest number.
3. The position of substituents is indicated by suitable numbers.
Ex: 2-Methyl propan-1-ol
The alcohols with two –OH groups are named as diols and alcohols with three –OH groups are named as triols.
Ex: Ethane – 1,2 – diol, propane -1,2,3-triol
Example:
Methyl Alcohol CH-3OH
Ehtyl alcohol C-2H-5OH also written as CH-3CH-2OH
Propyl alcohol C-3H-7OH also written as CH-3CH-2CH-2OH
They are classified according to the number of hydroxyl groups in the molecule.
i. Monohydric alcohol contains one -OH group.
ii. A dihydric alcohol contains two -OH groups in the molecule
ex. ethylene glycol
CH2OH
|
CH2OH
iii. A trihydric alcohol contains three -OH groups in its molecules
ex.glycerol
CH2OH
|
CH2OH
|
CH2OH
Monohydric alcohols are represented by the general formula R-OH or CnH2n+1OH.
Monohydric alcohols are further classified according to the carbon atom to which the hydroxyl group is attached.
1. Primary alcohols: -OH group is attached to primary carbon atom. They contain the group -CH2OH
eg.: CH3CH2OH, CH3CH2CH2OH
2. Secondry alcohol: -OH group is attached to a secondary carbon atom. It contains a divalent >CHOH group.
Ex. iso-propyl alcohol
3. Tertiary alcohol: -Oh group is attached to tertiary carbon atom. C-OH group is present
Alcohols – Nomenclature
Common system
Alcohols are named as alkyl alcohols. The alkyl group attached to the –OH group is named and the word alcohol is added to it.
Ex: Methyl alcohol
IUPAC nomenclature system
‘e’ in the parent chain is replaced by ‘ol’
Ex: Methanol
Rules follow for arriving at the names of alcohols
1. The longest continuous chain containing the carbon bonded to the OH group is selected as the parent chain.
2. The carbon atoms in the chain are numbered in such a way that the carbon atom carrying the hydroxyl group gets the lowest number.
3. The position of substituents is indicated by suitable numbers.
Ex: 2-Methyl propan-1-ol
The alcohols with two –OH groups are named as diols and alcohols with three –OH groups are named as triols.
Ex: Ethane – 1,2 – diol, propane -1,2,3-triol
Methods of Preparation of Alcohols
Methods of Preparation of Alcohols
1. Preparation from haloalkanes
2. By reduction of aldehydes, ketones and esters
3. From Grignard reagents
4. By hydrolysis of esters
5. From alkenes
i) Hydration of alkenes
ii) Hydroboratin oxidation reaction
iii) Oxymercuration - reduction
6. From aliphatic primary amines
Industrial Preparation
1. Hydration of alkenes
2. Oxo process
3. Fermentation of carbohydrates
4. Manufacture of methanol from water gas
1. Preparation from haloalkanes
2. By reduction of aldehydes, ketones and esters
3. From Grignard reagents
4. By hydrolysis of esters
5. From alkenes
i) Hydration of alkenes
ii) Hydroboratin oxidation reaction
iii) Oxymercuration - reduction
6. From aliphatic primary amines
Industrial Preparation
1. Hydration of alkenes
2. Oxo process
3. Fermentation of carbohydrates
4. Manufacture of methanol from water gas
Alcohols - physical Properties
A. Physical state: the lower members are colourless liquids and have a characteristic smell and burning taste.
The higher members(with more than 12 carbons) are colourless wax like solids.
B. Solubility: The lower members are highly soluble in water.
Amongst isomeric alcohols, the solubility increases with branching.
C. Alcohols exists associated molecules due to intermolecular hydrogen bonds.
D. Boiling points: The lowers members have low boiling points.
With the increase in molecular weight, the boiling points keep on increasing gradually.
e. Density: Generally alcohols are lighter than water.
Density of alcohols increases with molecular mass.
F. Alcohols have intoxicating effects.
Methanol is poisonous.
Ethanol is used for drinking purposes.
The higher members(with more than 12 carbons) are colourless wax like solids.
B. Solubility: The lower members are highly soluble in water.
Amongst isomeric alcohols, the solubility increases with branching.
C. Alcohols exists associated molecules due to intermolecular hydrogen bonds.
D. Boiling points: The lowers members have low boiling points.
With the increase in molecular weight, the boiling points keep on increasing gradually.
e. Density: Generally alcohols are lighter than water.
Density of alcohols increases with molecular mass.
F. Alcohols have intoxicating effects.
Methanol is poisonous.
Ethanol is used for drinking purposes.
Alcohols - Chemical Reactions
On the basis of structure of alcohols, their reactions may be divided into following types or groups for the purposes of study.
1. Reactions involving cleavage of oxygen-hydrogen bond.
2. Reactions involving cleavage of carbon-oxygen bond.
3. Reactions involving both the alkyl and hydroxyl groups.
1. Reactions involving cleavage of oxygen-hydrogen bond.
i) reaction with active metals
ii) reaction with metal hydrides
iii) reaction with carboxylic acids (esterification)
iv) reaction with Grignard reagents
v) Reaction with acyl chloride or acid anhydride (acylation)
2. Reactions involving cleavage of carbon-oxygen bond.
i) reaction with hydrogen haldies
ii) reaction with phosphorus halides
iii) reaction with thionyl chloride
3. Reactions involving both the alkyl and hydroxyl groups.
i) dehydration
ii) oxidation,
iii) dehydrogenation
reaction with ZnCl2/conc.-HCl, (Lucas test)
conversion of alcohols into aldehydes and ketones;
1. Reactions involving cleavage of oxygen-hydrogen bond.
2. Reactions involving cleavage of carbon-oxygen bond.
3. Reactions involving both the alkyl and hydroxyl groups.
1. Reactions involving cleavage of oxygen-hydrogen bond.
i) reaction with active metals
ii) reaction with metal hydrides
iii) reaction with carboxylic acids (esterification)
iv) reaction with Grignard reagents
v) Reaction with acyl chloride or acid anhydride (acylation)
2. Reactions involving cleavage of carbon-oxygen bond.
i) reaction with hydrogen haldies
ii) reaction with phosphorus halides
iii) reaction with thionyl chloride
3. Reactions involving both the alkyl and hydroxyl groups.
i) dehydration
ii) oxidation,
iii) dehydrogenation
reaction with ZnCl2/conc.-HCl, (Lucas test)
conversion of alcohols into aldehydes and ketones;
Alcohols -Reaction with active metals - acidic character
Alcohols are weakly acidic in nature.
They react with active metals such as sodium, potassium, magnesium, aluminium, etc. to liberate hydrogen gas and form metal alkoxide.
Liberation of hydrogen shows that alcohols are acidic in nature.
The acidic nature of alcohols is due to the presence of polar O-H bond.
As oxygen withdraws shared electron pair between O and H atoms towards itself, it can lose the proton (H+).
However, alcohols are weak acids
They react with active metals such as sodium, potassium, magnesium, aluminium, etc. to liberate hydrogen gas and form metal alkoxide.
Liberation of hydrogen shows that alcohols are acidic in nature.
The acidic nature of alcohols is due to the presence of polar O-H bond.
As oxygen withdraws shared electron pair between O and H atoms towards itself, it can lose the proton (H+).
However, alcohols are weak acids
Alcohols Esterification
Esterification
Alcohols react with monocarboxylic acids, in the presence of concentrated sulphuric acid or dry HCL gas as catalyst, to from esters. This reaction is known as esterification.
Alcohols react with monocarboxylic acids, in the presence of concentrated sulphuric acid or dry HCL gas as catalyst, to from esters. This reaction is known as esterification.
Alcohols Dehydration
Dehydration
When alcohols are heated with conc. or H3PO4, at 443 K, they get dehydrated to form alkenes.
The ease of dehydration of alcohol follows the order 3>2>1 which is also the order of stability of carbocation.
When alcohols are heated with conc. or H3PO4, at 443 K, they get dehydrated to form alkenes.
The ease of dehydration of alcohol follows the order 3>2>1 which is also the order of stability of carbocation.
Alcohols oxidation
Oxidation
The oxidation of alcohols can be carried out by a number of reagents such as acqueous, alkalineor acidified KMnO4, acidified Na2Cr2O7, nitric acid, chromic acid, etc.
The oxidation of alcohols can be carried out by a number of reagents such as acqueous, alkalineor acidified KMnO4, acidified Na2Cr2O7, nitric acid, chromic acid, etc.
Alcohols - Reaction with Sodium
Reaction with sodium
The cleavage in this reaction will be in the OH bond. Alcohols react with active metals to liberate hydrogen gas an form metal alkoxide.
Ethanol or Ethyl alcohol reacts with sodium to gibve Sodium ethoxide and hydrogen
The cleavage in this reaction will be in the OH bond. Alcohols react with active metals to liberate hydrogen gas an form metal alkoxide.
Ethanol or Ethyl alcohol reacts with sodium to gibve Sodium ethoxide and hydrogen
Alcohols - Reaction with phosphorus halides
. Reaction with phosphorus halides
Phosphorus halides such as PCl5, Pcl3, PBr3 and PI3 react with alcohols to form corresponding haloalkanes.
Phosphorus halides such as PCl5, Pcl3, PBr3 and PI3 react with alcohols to form corresponding haloalkanes.
Conversion of alcohols into aldehydes and ketones
Conversion of alcohols into aldehydes and ketones
Oxidation of primary alcohol gives aldehydes.
Oxidation of secondary alcohols gives ketones.
It is difficult to oxidize tertiary alcohols.
Oxidation of primary alcohol gives aldehydes.
Oxidation of secondary alcohols gives ketones.
It is difficult to oxidize tertiary alcohols.
Alkyl and Aryl Halides - Introduction, Nomenclature
When hydrogen atom or atoms of alkanes are replaced by the corresponding number of halogen atoms, the compounds are called halogen derivatives of alkanes.
They are classified according to the number of halogen atoms that replace hydrogen atoms in the alkane.
Monohalogen derivatives: They contain only one halogen atom.
e.g. CH-3Cl Methyl chloride
CH-3-CH-CH-3 2-Bromopropane
!
Br
Monohalogen derivatives of alkane are called alkyl halides
Dihalogen alkanes contain two halogen atoms.
Trihalog alkanes contain three halogen atoms.
Monohalo alkanes
The general formula is RX where is a alkyl group and X is a halogen.
Classification of Haloalkanes
A. Type of halogen atoms; Fluorides, chlorides, bromides, iodides
B. Number of halogena atoms, monohalo, dihalo, trihalo, tetra halo.
Classification of Haloalkanes
1. Compounds containing sp3 hybridization
2. Compounds containing sp2 hybridization
Compounds containing sp3 hybridization
a) halo alkances or alkyl halides
(i)Primary halogenoalkanes
In a primary (1°) halogenoalkane, the carbon which carries the halogen atom is only attached to one other alkyl group.
Secondary halogenoalkanes
In a secondary (2°) halogenoalkane, the carbon with the halogen attached is joined directly to two other alkyl groups, which may be the same or different.
Tertiary halogenoalkanes
In a tertiary (3°) halogenoalkane, the carbon atom holding the halogen is attached directly to three alkyl groups, which may be any combination of same or different.
b) Allylic halides: Halogens attached to alkenes to a carbon atom next to carbon-carbon double bond.
c) Benzylic halide (aralalkyl halide): Halogens attached to alkenes to a carbon atom next to to an aromatic ring (not to a carbon atom in the aromatic ring). It is attached to a carbon atom which is inturn attached to a carbon atom in the aromatic ring.
2. Compounds containing sp2 hybridization
a) Vinylic halides: Halogens attached to alkenes to a carbon atom of one of the carbon atoms of a double bond.
B) Aryl halides: Halogens attached to alkenes to a carbon atom of an aromatic ring
Nomenclature – Alkyl and Aryl halides
Nomenclature of alkyl halides
Common system
The monohalogen derivatives of alkanes are called alkyl halides. These are named by naming the alkyl group attached to halogen and adding the name of the halide.
Ex: Methyl halide, Isobutyl halide
The name of the alkyl group and halide are written as two separate words. The prefixes used to distinguish alkanes like n-, iso-, sec-, tert, etc. are also written.
IUPAC System
The monohalogen derivatives of alkanes are called haloalkanes.
The names of haloalkanes are written by prefixing the word ‘halo’ (bromo or chloro or iodo or fluoro) to the name of the alkane corresponding to the longest continuous carbon chain holding the halogen atom.
Ex: Bromoethane
Rules for naming haloalkanes having branches in carbon chains
1. The longest continuous chain containing the carbon attached to halogen group is selected as the parent alkane (principal chain or parent chain). In naming alkanes all rules that apply to alkane names are to be followed.
2. The carbon atoms are numbered in such a way that the carbon atom carrying the halogen atom gets the lowest number.
3. The position of the halogen atom and other substituents are indicated by numbers 1,2,3… etc.
Ex: 1-Iodo-2-methylpropane
Dihalo derivatives
1. When both the halogen atoms are attached to the same C-atom, these are called geminal dihalides. Alkylidene dihalides or alkylidene halides are also names used for such compounds.
Ex: ethlydine dichloride
2. When the two halogen atoms are in adjacent C-atoms, they are called vicinal dihalides. They are prepared from alkenes and hence they are named as the dihalide of the alkene from which they are prepared.
Ex: ethylene dichloride
Polyhalo derivatives
Ex: Trichloromethane
Fully halogenated hydrocarbons are also called perhalohydrocarbons under common system.
Nomenclature of aryl halides
Aryl halides are termed Haloarenes in IUPAC systems. The prefix ‘halo” ((bromo or chloro or iodo or fluoro) is placed before the name of the aromatic hydrocarbon. In case of disubstituted compounds, the relative positions are indicated by (1,2), (1,3) or (1,4). Ortho, meta and para are also used to indicate the positions.
Ex: Chlorobenzene, Bromobenzene
They are classified according to the number of halogen atoms that replace hydrogen atoms in the alkane.
Monohalogen derivatives: They contain only one halogen atom.
e.g. CH-3Cl Methyl chloride
CH-3-CH-CH-3 2-Bromopropane
!
Br
Monohalogen derivatives of alkane are called alkyl halides
Dihalogen alkanes contain two halogen atoms.
Trihalog alkanes contain three halogen atoms.
Monohalo alkanes
The general formula is RX where is a alkyl group and X is a halogen.
Classification of Haloalkanes
A. Type of halogen atoms; Fluorides, chlorides, bromides, iodides
B. Number of halogena atoms, monohalo, dihalo, trihalo, tetra halo.
Classification of Haloalkanes
1. Compounds containing sp3 hybridization
2. Compounds containing sp2 hybridization
Compounds containing sp3 hybridization
a) halo alkances or alkyl halides
(i)Primary halogenoalkanes
In a primary (1°) halogenoalkane, the carbon which carries the halogen atom is only attached to one other alkyl group.
Secondary halogenoalkanes
In a secondary (2°) halogenoalkane, the carbon with the halogen attached is joined directly to two other alkyl groups, which may be the same or different.
Tertiary halogenoalkanes
In a tertiary (3°) halogenoalkane, the carbon atom holding the halogen is attached directly to three alkyl groups, which may be any combination of same or different.
b) Allylic halides: Halogens attached to alkenes to a carbon atom next to carbon-carbon double bond.
c) Benzylic halide (aralalkyl halide): Halogens attached to alkenes to a carbon atom next to to an aromatic ring (not to a carbon atom in the aromatic ring). It is attached to a carbon atom which is inturn attached to a carbon atom in the aromatic ring.
2. Compounds containing sp2 hybridization
a) Vinylic halides: Halogens attached to alkenes to a carbon atom of one of the carbon atoms of a double bond.
B) Aryl halides: Halogens attached to alkenes to a carbon atom of an aromatic ring
Nomenclature – Alkyl and Aryl halides
Nomenclature of alkyl halides
Common system
The monohalogen derivatives of alkanes are called alkyl halides. These are named by naming the alkyl group attached to halogen and adding the name of the halide.
Ex: Methyl halide, Isobutyl halide
The name of the alkyl group and halide are written as two separate words. The prefixes used to distinguish alkanes like n-, iso-, sec-, tert, etc. are also written.
IUPAC System
The monohalogen derivatives of alkanes are called haloalkanes.
The names of haloalkanes are written by prefixing the word ‘halo’ (bromo or chloro or iodo or fluoro) to the name of the alkane corresponding to the longest continuous carbon chain holding the halogen atom.
Ex: Bromoethane
Rules for naming haloalkanes having branches in carbon chains
1. The longest continuous chain containing the carbon attached to halogen group is selected as the parent alkane (principal chain or parent chain). In naming alkanes all rules that apply to alkane names are to be followed.
2. The carbon atoms are numbered in such a way that the carbon atom carrying the halogen atom gets the lowest number.
3. The position of the halogen atom and other substituents are indicated by numbers 1,2,3… etc.
Ex: 1-Iodo-2-methylpropane
Dihalo derivatives
1. When both the halogen atoms are attached to the same C-atom, these are called geminal dihalides. Alkylidene dihalides or alkylidene halides are also names used for such compounds.
Ex: ethlydine dichloride
2. When the two halogen atoms are in adjacent C-atoms, they are called vicinal dihalides. They are prepared from alkenes and hence they are named as the dihalide of the alkene from which they are prepared.
Ex: ethylene dichloride
Polyhalo derivatives
Ex: Trichloromethane
Fully halogenated hydrocarbons are also called perhalohydrocarbons under common system.
Nomenclature of aryl halides
Aryl halides are termed Haloarenes in IUPAC systems. The prefix ‘halo” ((bromo or chloro or iodo or fluoro) is placed before the name of the aromatic hydrocarbon. In case of disubstituted compounds, the relative positions are indicated by (1,2), (1,3) or (1,4). Ortho, meta and para are also used to indicate the positions.
Ex: Chlorobenzene, Bromobenzene
IIT JEE Revision - Alkyl and Aryl Halides - Methods of preparation
Methods of preparation
1. From hydrocarbons
a) from alkanes: halogens react with alkanes in the presence of uv light to form haloalkanes.
b) from alkenes: by the electrophylic addition of halogen acids (HBr, HCl, or HI)
Markownikov rule and anti Markownikov rule are applicable in the reaction between alkene and halogen acids.
2. From alcohols:
This is the most widely used method for the preparation of haloalkanes in the laboratory.
Methods preparing alkyl halides from alcohols
(i) By the action of halogen acids on alcohols
(a) Chloro alkanes: Primary and secondary alcohols form chloroalkanes when hydrochloric acid gas is passed through alcohol in the presence of anhydrous zinc chloride (Groove's process).
ZnCl2 is a Lewis acid.
(b) Tertiary alcohols are very reactive and therefore, they react readily with conc. HCl even in the absence of zinc chloride.
(c) Bromo alkanes: Bromoalkanes are obtained by heating an alcohol with hydrobromic acid (48%) in the presence of a little conc. H2SO4 whihc acts as a catalyst.
Hydrobromic acid (HBR) can be generated in situ (during the reaction itself) by the action of conc. H2SO4 on KBr or NaBr.
(d) Iodoalkanes: are obtained by heating alcohols with constant boiling hydroiodic acid (57%).
Hydroiodic acid (HI) can be generated in situ (during the reaction itself) by the action of phosporic acid on potassium iodide.
Note: Unlike alkyl chlorides, secondary andd tertiary bromides and iodides cannot be prepared from respective alcohols because the secondary and tertiary alcohols on heating with H2SO4 undergo dehydration to form alkenes.
Hydrogen fluoride is the least reactive of the hydrogen halides and the preparation of fluroalkanes is not practical by using alcohol and hydrogen fluoride.
(ii) Reaction of alcohols with phosphorus halides
Phosphorus halides such as PCl5, PCl3, PBr3 and PI3 react with alcohols to form corresponding haloalkanes.
(a) Chloroalkanes can be prepared by the action of phosphorus pentachloride or phosphorous trichloride on alcohols.
(b)Bromoalkanes and iodoalkanes are prepared by the action of phosphorous bromide and phosphorous tri-iodide respectively on alcohols.
phosphorous bromide and phosphorous iodide are not very stable compounds. Hence there are generally prepared in situ (during the reaction) by the action of red phosphorous on
Haloalkanes : Chloroethane, Bromoethane, Iodoethane
Reaction with ZnCl2/conc.-HCl
This is a reaction or test to distinguish various categories of alcohols and is termed Lucas test.
In this test, an alcohol is treated with an equimolar mixture of concentrated hydrochloric acid and anhydrous ZnCl2 (called Lucas reagent).
Alcohols get converted into alkylhalides. As alkyl halides are insoluble in water, their presence is indicated by the appearance of turbidity in the reaction mixture. Br2 or I2.
(iii) By the action of thionyl chloride on alcohol
Chloroalkanes can be prepared from alcohols by refluxing alcohols with thionyl chloride in the presence of pyridine.
3. By Halide Exchange
This reaction is particularly useful for preparing iodoalkanes.
The iodoalkanes are obtained by heating chloro or bromo alkanes with a concentrated solution of sodium iodide in acetone.
The reaction gives the best results with primary halides. This reaction is known as Finkelstein reaction.
Fluoro alkanes are difficult to prepare by other methods. They are prepared by treating alkyl chlorides or bromides with salts such as mecurous fluoride (Hg2F2), silver fluoride (AgF), cobalt fluoride (CoF3) or antimony trifluoride (SbF3). This reaction is known as Swarts reaction.
cobalt fluoride (CoF3) or antimony trifluoride (SbF3) are used when the organic halides contain two or three halogen atoms on the same carbon atom.
4. Preparation of alkyl halides from silver salts of acids.
The silver salts of the carboxylic acids dissolved in CCl4 are decomposed by bromine to form bromoalkanes. This reaction is called Borodine Hundsdiecker reaction.
Chloroalkanes can also be obtained by this method by using Cl2 instead of Br2, but the yield of chloroalkanes is very poor.
Iodo alkanes cannot be obtained by this reaction.
1. From hydrocarbons
a) from alkanes: halogens react with alkanes in the presence of uv light to form haloalkanes.
b) from alkenes: by the electrophylic addition of halogen acids (HBr, HCl, or HI)
Markownikov rule and anti Markownikov rule are applicable in the reaction between alkene and halogen acids.
2. From alcohols:
This is the most widely used method for the preparation of haloalkanes in the laboratory.
Methods preparing alkyl halides from alcohols
(i) By the action of halogen acids on alcohols
(a) Chloro alkanes: Primary and secondary alcohols form chloroalkanes when hydrochloric acid gas is passed through alcohol in the presence of anhydrous zinc chloride (Groove's process).
ZnCl2 is a Lewis acid.
(b) Tertiary alcohols are very reactive and therefore, they react readily with conc. HCl even in the absence of zinc chloride.
(c) Bromo alkanes: Bromoalkanes are obtained by heating an alcohol with hydrobromic acid (48%) in the presence of a little conc. H2SO4 whihc acts as a catalyst.
Hydrobromic acid (HBR) can be generated in situ (during the reaction itself) by the action of conc. H2SO4 on KBr or NaBr.
(d) Iodoalkanes: are obtained by heating alcohols with constant boiling hydroiodic acid (57%).
Hydroiodic acid (HI) can be generated in situ (during the reaction itself) by the action of phosporic acid on potassium iodide.
Note: Unlike alkyl chlorides, secondary andd tertiary bromides and iodides cannot be prepared from respective alcohols because the secondary and tertiary alcohols on heating with H2SO4 undergo dehydration to form alkenes.
Hydrogen fluoride is the least reactive of the hydrogen halides and the preparation of fluroalkanes is not practical by using alcohol and hydrogen fluoride.
(ii) Reaction of alcohols with phosphorus halides
Phosphorus halides such as PCl5, PCl3, PBr3 and PI3 react with alcohols to form corresponding haloalkanes.
(a) Chloroalkanes can be prepared by the action of phosphorus pentachloride or phosphorous trichloride on alcohols.
(b)Bromoalkanes and iodoalkanes are prepared by the action of phosphorous bromide and phosphorous tri-iodide respectively on alcohols.
phosphorous bromide and phosphorous iodide are not very stable compounds. Hence there are generally prepared in situ (during the reaction) by the action of red phosphorous on
Haloalkanes : Chloroethane, Bromoethane, Iodoethane
Reaction with ZnCl2/conc.-HCl
This is a reaction or test to distinguish various categories of alcohols and is termed Lucas test.
In this test, an alcohol is treated with an equimolar mixture of concentrated hydrochloric acid and anhydrous ZnCl2 (called Lucas reagent).
Alcohols get converted into alkylhalides. As alkyl halides are insoluble in water, their presence is indicated by the appearance of turbidity in the reaction mixture. Br2 or I2.
(iii) By the action of thionyl chloride on alcohol
Chloroalkanes can be prepared from alcohols by refluxing alcohols with thionyl chloride in the presence of pyridine.
3. By Halide Exchange
This reaction is particularly useful for preparing iodoalkanes.
The iodoalkanes are obtained by heating chloro or bromo alkanes with a concentrated solution of sodium iodide in acetone.
The reaction gives the best results with primary halides. This reaction is known as Finkelstein reaction.
Fluoro alkanes are difficult to prepare by other methods. They are prepared by treating alkyl chlorides or bromides with salts such as mecurous fluoride (Hg2F2), silver fluoride (AgF), cobalt fluoride (CoF3) or antimony trifluoride (SbF3). This reaction is known as Swarts reaction.
cobalt fluoride (CoF3) or antimony trifluoride (SbF3) are used when the organic halides contain two or three halogen atoms on the same carbon atom.
4. Preparation of alkyl halides from silver salts of acids.
The silver salts of the carboxylic acids dissolved in CCl4 are decomposed by bromine to form bromoalkanes. This reaction is called Borodine Hundsdiecker reaction.
Chloroalkanes can also be obtained by this method by using Cl2 instead of Br2, but the yield of chloroalkanes is very poor.
Iodo alkanes cannot be obtained by this reaction.
Alkyl and Aryl Halides - Physical Properties
Physical properties of halogenoalkanes
Boiling Points
the only methyl halide which is a liquid is iodomethane;
chloroethane is a gas.
The examples show that the boiling points fall as the isomers go from a primary to a secondary to a tertiary halogenoalkane. This is a simple result of the fall in the effectiveness of the dispersion forces.
Solubility in water
The halogenoalkanes are at best only very slightly soluble in water.
In order for a halogenoalkane to dissolve in water you have to break attractions between the halogenoalkane molecules (van der Waals dispersion and dipole-dipole interactions) and break the hydrogen bonds between water molecules. Both of these cost energy.
Solubility in organic solvents
Halogenoalkanes tend to dissolve in organic solvents because the new intermolecular attractions have much the same strength as the ones being broken in the separate halogenoalkane and solvent.
bond strength falls as you go from C-F to C-I, and notice how much stronger the carbon-fluorine bond is than the rest.
In order for anything to react with the halogenoalkanes, the carbon-halogen bond has got to be broken. Because that gets easier as you go from fluoride to chloride to bromide to iodide, the compounds get more reactive in that order.
Iodoalkanes are the most reactive and fluoroalkanes are the least. In fact, fluoroalkanes are so unreactive that we shall pretty well ignore them completely in discussion on reactions.
Boiling Points
the only methyl halide which is a liquid is iodomethane;
chloroethane is a gas.
The examples show that the boiling points fall as the isomers go from a primary to a secondary to a tertiary halogenoalkane. This is a simple result of the fall in the effectiveness of the dispersion forces.
Solubility in water
The halogenoalkanes are at best only very slightly soluble in water.
In order for a halogenoalkane to dissolve in water you have to break attractions between the halogenoalkane molecules (van der Waals dispersion and dipole-dipole interactions) and break the hydrogen bonds between water molecules. Both of these cost energy.
Solubility in organic solvents
Halogenoalkanes tend to dissolve in organic solvents because the new intermolecular attractions have much the same strength as the ones being broken in the separate halogenoalkane and solvent.
bond strength falls as you go from C-F to C-I, and notice how much stronger the carbon-fluorine bond is than the rest.
In order for anything to react with the halogenoalkanes, the carbon-halogen bond has got to be broken. Because that gets easier as you go from fluoride to chloride to bromide to iodide, the compounds get more reactive in that order.
Iodoalkanes are the most reactive and fluoroalkanes are the least. In fact, fluoroalkanes are so unreactive that we shall pretty well ignore them completely in discussion on reactions.
Alkyl and Aryl Halides - CHEMICAL REACTIONS
Haloalkanes are one of the most reactive classes of organic compounds. Many organic compounds are prepared using alkyl halides. So alkyl halides are considered as synthetic tools in the hands of an organic chemist to synthesize various compounds.
The reactions of alkyl halides can be grouped under the following heads for a study of them.
Nucleophilic substitution reactions
Elimination reactions
Reactions with metals
Reduction
Nucleophilic substitution reactions
1. Substitution by hydroxylgroup (OH) leads to the formation of alcohols
2. Substitution by alkoxy group leads to the formation of ether.
3. Substitution by cyano group leads to the formation of cyanides or nitriles.
4. Substitution by isocyanide group leads to the formation of isocyanides.
When haloalkane is treated with alcoholic silver cyanide (AgCN), isocynaides (R-N≡C) are obtained. They are also called carbyl amines.
RX + AgCN ---> RNC + AGX
C2H5Br + AgCN ---> C2H5NC + Ag Br
5. Substitution by amino group leads to the formation of amines.
6. Substitution by nitrite group leads to the formation of nitrite.
7. Substitution by nitro group leads to the formation of nitro alkanes.
8. Substitution by carboxyl group leads to the formation of esters.
9. substitution by hydrosulphide group leads to the formation of thioalcohols.
10. Substitution by mercaptide group leads to the formation of thioethers.
11. Substitution by alkyl group leads to the formation of alkynes.
Elimination reactions (Dehydrohalogenation)
In this reaction alkenes are formed.
This reaction occus when alkyl halides are boiled iwth alcoholic solution of potassium hydroxide. One hydrogen atom and one halogen atom are removed and a double bond forms.
Reaction with active metals
Active metals like sodium, magnesium, cadmium, lithium combine with alkyl halides to give compounds containing carbon metal bonds (called as organometallic compounds).
i) With magnesium, alkyl magnesium halide is formed. This is called as Grignard reagent.
ii)Two molecules of alkyl halides react with sodium in the presence of ether and form alkanes. The reaction is termed Wurtz reaction and is used to prepare symmetrical alkanes
Reduction
Haloalkanes can be reduced to alkanes by some reagents. The reagents include
i) Hydrogen in the presence of a metal catalyst such as nickel, palladium or platinum.
ii)zinc copper couple and ethyl alcohol
iii) Hydroiodic acid in the presence of red phosphorus
Rearrangement
When a haloalkance is heated at 573 K or at a slightly lower temperature in the presence
of anhydrous aluminium chloride as catalyst, the halide undergoes rearrangement to form isomeric haloalkane. So this reaction is an isomerism reaction.
The reactions of alkyl halides can be grouped under the following heads for a study of them.
Nucleophilic substitution reactions
Elimination reactions
Reactions with metals
Reduction
Nucleophilic substitution reactions
1. Substitution by hydroxylgroup (OH) leads to the formation of alcohols
2. Substitution by alkoxy group leads to the formation of ether.
3. Substitution by cyano group leads to the formation of cyanides or nitriles.
4. Substitution by isocyanide group leads to the formation of isocyanides.
When haloalkane is treated with alcoholic silver cyanide (AgCN), isocynaides (R-N≡C) are obtained. They are also called carbyl amines.
RX + AgCN ---> RNC + AGX
C2H5Br + AgCN ---> C2H5NC + Ag Br
5. Substitution by amino group leads to the formation of amines.
6. Substitution by nitrite group leads to the formation of nitrite.
7. Substitution by nitro group leads to the formation of nitro alkanes.
8. Substitution by carboxyl group leads to the formation of esters.
9. substitution by hydrosulphide group leads to the formation of thioalcohols.
10. Substitution by mercaptide group leads to the formation of thioethers.
11. Substitution by alkyl group leads to the formation of alkynes.
Elimination reactions (Dehydrohalogenation)
In this reaction alkenes are formed.
This reaction occus when alkyl halides are boiled iwth alcoholic solution of potassium hydroxide. One hydrogen atom and one halogen atom are removed and a double bond forms.
Reaction with active metals
Active metals like sodium, magnesium, cadmium, lithium combine with alkyl halides to give compounds containing carbon metal bonds (called as organometallic compounds).
i) With magnesium, alkyl magnesium halide is formed. This is called as Grignard reagent.
ii)Two molecules of alkyl halides react with sodium in the presence of ether and form alkanes. The reaction is termed Wurtz reaction and is used to prepare symmetrical alkanes
Reduction
Haloalkanes can be reduced to alkanes by some reagents. The reagents include
i) Hydrogen in the presence of a metal catalyst such as nickel, palladium or platinum.
ii)zinc copper couple and ethyl alcohol
iii) Hydroiodic acid in the presence of red phosphorus
Rearrangement
When a haloalkance is heated at 573 K or at a slightly lower temperature in the presence
of anhydrous aluminium chloride as catalyst, the halide undergoes rearrangement to form isomeric haloalkane. So this reaction is an isomerism reaction.
Alkyl and Aryl Halides - Rearrangement reactions of alkyl carbocation
When a haloalkance is heated at 573 K or at a slightly lower temperature in the presence of anhydrous aluminium chloride as catalyst, the halide undergoes rearrangement to form isomeric haloalkane. So this reaction is an isomerism reaction.
1-Chloropropane CH3CH2CH2Cl rearranges to 2-Chloropropane. Chlorine is attached to the 2nd carbon (or middle carbon) instead of the 1st carbon or terminal carbon
If there is no hydrogen atom on the carbon adjacent to the C-X group, rearrangment occurs and methyl group migrates providing the opportunity for the halogen atom to occupy the position.
1-Chloro-2,2 dimethyl propane rearranges to 2-Chloro-2-methylbutane
1-Chloropropane CH3CH2CH2Cl rearranges to 2-Chloropropane. Chlorine is attached to the 2nd carbon (or middle carbon) instead of the 1st carbon or terminal carbon
If there is no hydrogen atom on the carbon adjacent to the C-X group, rearrangment occurs and methyl group migrates providing the opportunity for the halogen atom to occupy the position.
1-Chloro-2,2 dimethyl propane rearranges to 2-Chloro-2-methylbutane
Alkyl and Aryl Halides Grignard reactions
A solution of an alkyl halide in dry ether reacts with magnesium to form alkyl magnesium halide.
RX + Mg in dry ether --> RMGX
RMgX compounds are known as Grignard reagents. They were discovered by Victor Grignard, a French National. He got the Nobel prize in Chemistry in 1912.
These compounds have many synthetic applications and are used in the preparation of many organic compounds.
Vinyl and aryl halides also form magnesium halides.
RX + Mg in dry ether --> RMGX
RMgX compounds are known as Grignard reagents. They were discovered by Victor Grignard, a French National. He got the Nobel prize in Chemistry in 1912.
These compounds have many synthetic applications and are used in the preparation of many organic compounds.
Vinyl and aryl halides also form magnesium halides.
Alkyl and Aryl Halides - Nucleophilic substitution reactions
Nucleophilic substitution in primary halogenoalkanes
The nucleophilic substitution reaction - an SN2 reaction - S stands for substitution, N for nucleophilic, and the 2 is order of reaction. It is because the initial stage of the reaction involves two species - the bromoethane and the Nucleophilic (Nu-) ion.
Nucleophilic substitution in tertiary halogenoalkanes - The nucleophilic substitution reaction - an SN1 reaction (1 denotes 1st order)
Many organic compounds are prepared using alkyl halides
Nucleophilic substitution reactions
1. Substitution by hydroxylgroup (OH) leads to the formation of alcohols
2. Substitution by alkoxy group leads to the formation of ether.
3. Substitution by cyano group leads to the formation of cyanides or nitriles.
4. Substitution by isocyanide group leads to the formation of isocyanides.
When haloalkane is treated with alcoholic silver cyanide (AgCN), isocynaides (R-N≡C) are obtained. They are also called carbyl amines.
RX + AgCN ---> RNC + AGX
C2H5Br + AgCN ---> C2H5NC + Ag Br
5. Substitution by amino group leads to the formation of amines.
6. Substitution by nitrite group leads to the formation of nitrite.
7. Substitution by nitro group leads to the formation of nitro alkanes.
8. Substitution by carboxyl group leads to the formation of esters.
9. substitution by hydrosulphide group leads to the formation of thioalcohols.
10. Substitution by mercaptide group leads to the formation of thioethers.
11. Substitution by alkyl group leads to the formation of alkynes.
The nucleophilic substitution reaction - an SN2 reaction - S stands for substitution, N for nucleophilic, and the 2 is order of reaction. It is because the initial stage of the reaction involves two species - the bromoethane and the Nucleophilic (Nu-) ion.
Nucleophilic substitution in tertiary halogenoalkanes - The nucleophilic substitution reaction - an SN1 reaction (1 denotes 1st order)
Many organic compounds are prepared using alkyl halides
Nucleophilic substitution reactions
1. Substitution by hydroxylgroup (OH) leads to the formation of alcohols
2. Substitution by alkoxy group leads to the formation of ether.
3. Substitution by cyano group leads to the formation of cyanides or nitriles.
4. Substitution by isocyanide group leads to the formation of isocyanides.
When haloalkane is treated with alcoholic silver cyanide (AgCN), isocynaides (R-N≡C) are obtained. They are also called carbyl amines.
RX + AgCN ---> RNC + AGX
C2H5Br + AgCN ---> C2H5NC + Ag Br
5. Substitution by amino group leads to the formation of amines.
6. Substitution by nitrite group leads to the formation of nitrite.
7. Substitution by nitro group leads to the formation of nitro alkanes.
8. Substitution by carboxyl group leads to the formation of esters.
9. substitution by hydrosulphide group leads to the formation of thioalcohols.
10. Substitution by mercaptide group leads to the formation of thioethers.
11. Substitution by alkyl group leads to the formation of alkynes.
IIT JEE Revision - Ch.27 Aldehydes and Ketones - Core Points
syllabus
Aldehydes and Ketones:
Preparation, Physical properties and chemical properties
oxidation,
reduction,
oxime and
hydrazone formation;
aldol condensation,
Perkin reaction;
Cannizzaro reaction;
haloform reaction and
nucleophilic addition reactions (Grignard addition);
--------
Aldehydes contain carbonyl group C=O as functional group and the carbonyl atom carries at least one H atom.
Ketones
In ketones, also carbonyl group C=O is the functional group. But the carbonyl carbon does not contain any H atoms, but it is attached to two alkyl or aryl groups.
Getting an aldehyde from methylbenzene - by oxidation
Getting ketone from alcohols - By oxidation of secondary alcohols
Aldehydes and ketones are polar molecules because the C=O bond has a
dipole moment:
• Their polarity makes aldehydes and ketones have higher boiling points than
alkenes of similar molecular weight.
Oxidation
Carbonyl groups in aldehydes and ketones may be oxidized to form
compounds at the next “oxidation level”, that of carboxylic acids
Addition Using Grignard Reagents• Primary, secondary and tertiary alcohols may be formed in the reactions of
aldehydes or ketones with Grignard reagents.
http://www.cem.msu.edu/~reusch/VirtualText/aldket1.htm
Aldehydes and Ketones:
Preparation, Physical properties and chemical properties
oxidation,
reduction,
oxime and
hydrazone formation;
aldol condensation,
Perkin reaction;
Cannizzaro reaction;
haloform reaction and
nucleophilic addition reactions (Grignard addition);
--------
Aldehydes contain carbonyl group C=O as functional group and the carbonyl atom carries at least one H atom.
Ketones
In ketones, also carbonyl group C=O is the functional group. But the carbonyl carbon does not contain any H atoms, but it is attached to two alkyl or aryl groups.
Getting an aldehyde from methylbenzene - by oxidation
Getting ketone from alcohols - By oxidation of secondary alcohols
Aldehydes and ketones are polar molecules because the C=O bond has a
dipole moment:
• Their polarity makes aldehydes and ketones have higher boiling points than
alkenes of similar molecular weight.
Oxidation
Carbonyl groups in aldehydes and ketones may be oxidized to form
compounds at the next “oxidation level”, that of carboxylic acids
Addition Using Grignard Reagents• Primary, secondary and tertiary alcohols may be formed in the reactions of
aldehydes or ketones with Grignard reagents.
http://www.cem.msu.edu/~reusch/VirtualText/aldket1.htm
Aldehydes - Ketones - Introduction and Nomenclature
Aldehydes contain carbonyl group C=O as functional group and the carbonyl atom carries at least one H atom.
Ketones
In ketones, also carbonyl group C=O is the functional group. But the carbonyl carbon does not contain any H atoms, but it is attached to two alkyl or aryl groups.
Getting an aldehyde from methylbenzene - by oxidation
Getting ketone from alcohols - By oxidation of secondary alcohols
Aldehydes and ketones are polar molecules because the C=O bond has a
dipole moment:
• Their polarity makes aldehydes and ketones have higher boiling points than
alkenes of similar molecular weight.
Aldehydes and Ketones – Nomenclature
Nomenclature of Aliphatic Aldehydes
Common system
Aldehydes are named according to the name of the corresponding acid which they form on oxidation.
The suffix –ic acid of the name of the acid is replaced by aldehyde.
Ex: The aldehyde that gives acetic acid is termed as acetaldehyde.
Braching in the aldehyde chain, is indicated by carbon atom positions α, β, γ, δ.
The carbon atom next to the carbonyl carbon is assigned the letter α. The carbon next to α-carbon is the β-carbon. The carbon next to β-carbon is the γ-carbon. The carbon next to γ-carbon is the δ Carbon.
δ - γ- β- α carbons
C-C-C-C-CHO
Ex: α-Methyl butyraldehyde
IUPAC system
Aldehydes are termed alkanals. The terminal ‘e’ of the name of corresponding alkane is replaced by ‘al’.
Ex: methanal, ethanal, propanal.
Nomenclature for Aldehydes with Branches
1. The longest chain containing –CHO group is considered as the parent chain and the name is derived as an alkanal.
2. To determine the number of the carbon where a substituent is attached to the aldehyde chain, the carbons in the chain are numbered in such a way that the aldehydic group carbon gets lowest number (i.e 1). In other words number of the aldehydic chain carbons is started from the carbon in the carbonyl group.
Nomenclature of Aromatic Aldehydes
The simplest aromatic aldehyde is benzaldehyde. In aromatic aldehydes, -CHO group is directly attached to the benzene ring.
In case of substituted aromatic aldehydes, the positions of the substituents in benzene ring with respect to –CHO group are indicated either by suffixes ortho, meta or para or by numbers 1,2,3… etc. with the carbon bearing the –CHO group as number 1.
Ex; 2-Hydroxybenaldehyde – OH is the substituent at the 2 carbon from CHO group.
The aldehydic group (CHO) can be a part of the side chain. In other words, an aldehydic group may be attached to benzene ring.
The name will be as an example 2-Phenylethanal. In this compound CH2CHO is attached to a benzene ring. The substituent is ethanal group, and the numbering of carbon atoms still starts from CHO group carbon and the terminology indicates that a benzyl group is attached to ethanal at 2nd carbon.
Nomenclature of Ketones
Common system
Ketones are named by using the names of alkyl groups present in the molecule.
Ex: Dimethyl ketone, Methyl isopropyl ketone
IUPAC system
Ketones are termed as alkanones.
Rules for arriving at names
1. The longest chain carrying the carbonyl groupis considered as the parent chain and the name is derived by replacing the terminal ‘e’ of the name of the corresponding alkane by letters ‘one’.
Ex: Propanone
2. In case of substituted ketones, theparent chain is numbered in such a way that the ketone group carbon gets the lowest number (but the numbering does not start from ketone group carbon – caron attached with a double bond to oxygen).
3. The position of carbonyl group and the substituents is indicated by numbers.
Ex: 3-methylbutan-2-one (indicated that there is methyl group at 3rd carbon and carbonyl group at 2nd carbon on butanone.
Compounds having both aldehyde and ketone groups.
For compounds having both aldehyde and ketone groups, the aldehyde group is considered as the principal functional group and ketonic group is regarded as substituent. It is named as prefix oxo- along with a number to indicate its position.
Ex: 2-Methyl-4-oxohexanal
Aromatic Ketones
Purely aromatic or mixed aromatics ketones are know by their common names.
Examples
Acetophenone – Methyl phenyl ketone
Propiophenone – Ethyl phenyl ketone
Benzophenone - Diphenyle ketone
IUPAC 1993 recommendation for 3 same functional groups
If an unbranched chain is directly bonded to more than two same functional groups, the organic compound is named as a derivative of parent alkane which does not include the carbon atoms of the functional groups. These compounds are named by use of suffix tricarboaldehyde (for three –CHO groups).
Ex: Butane-1,2,4-tricarbaldehyde
If three groups are not directly bonded to the unbranched carbon chain, the two like groups are considered in the parent chain and are named by using di before the name of the functional group. The third group forming the side chain is considered as a substituent group.
Ex: 3-Formylmethylhexane-1,6-dial (three –CHO groups are there. But at 1 and 6 they are directly bonded. At three there is a branching of the alkane chain and –CHO is attached to the methyl group of the branch).
Ketones
In ketones, also carbonyl group C=O is the functional group. But the carbonyl carbon does not contain any H atoms, but it is attached to two alkyl or aryl groups.
Getting an aldehyde from methylbenzene - by oxidation
Getting ketone from alcohols - By oxidation of secondary alcohols
Aldehydes and ketones are polar molecules because the C=O bond has a
dipole moment:
• Their polarity makes aldehydes and ketones have higher boiling points than
alkenes of similar molecular weight.
Aldehydes and Ketones – Nomenclature
Nomenclature of Aliphatic Aldehydes
Common system
Aldehydes are named according to the name of the corresponding acid which they form on oxidation.
The suffix –ic acid of the name of the acid is replaced by aldehyde.
Ex: The aldehyde that gives acetic acid is termed as acetaldehyde.
Braching in the aldehyde chain, is indicated by carbon atom positions α, β, γ, δ.
The carbon atom next to the carbonyl carbon is assigned the letter α. The carbon next to α-carbon is the β-carbon. The carbon next to β-carbon is the γ-carbon. The carbon next to γ-carbon is the δ Carbon.
δ - γ- β- α carbons
C-C-C-C-CHO
Ex: α-Methyl butyraldehyde
IUPAC system
Aldehydes are termed alkanals. The terminal ‘e’ of the name of corresponding alkane is replaced by ‘al’.
Ex: methanal, ethanal, propanal.
Nomenclature for Aldehydes with Branches
1. The longest chain containing –CHO group is considered as the parent chain and the name is derived as an alkanal.
2. To determine the number of the carbon where a substituent is attached to the aldehyde chain, the carbons in the chain are numbered in such a way that the aldehydic group carbon gets lowest number (i.e 1). In other words number of the aldehydic chain carbons is started from the carbon in the carbonyl group.
Nomenclature of Aromatic Aldehydes
The simplest aromatic aldehyde is benzaldehyde. In aromatic aldehydes, -CHO group is directly attached to the benzene ring.
In case of substituted aromatic aldehydes, the positions of the substituents in benzene ring with respect to –CHO group are indicated either by suffixes ortho, meta or para or by numbers 1,2,3… etc. with the carbon bearing the –CHO group as number 1.
Ex; 2-Hydroxybenaldehyde – OH is the substituent at the 2 carbon from CHO group.
The aldehydic group (CHO) can be a part of the side chain. In other words, an aldehydic group may be attached to benzene ring.
The name will be as an example 2-Phenylethanal. In this compound CH2CHO is attached to a benzene ring. The substituent is ethanal group, and the numbering of carbon atoms still starts from CHO group carbon and the terminology indicates that a benzyl group is attached to ethanal at 2nd carbon.
Nomenclature of Ketones
Common system
Ketones are named by using the names of alkyl groups present in the molecule.
Ex: Dimethyl ketone, Methyl isopropyl ketone
IUPAC system
Ketones are termed as alkanones.
Rules for arriving at names
1. The longest chain carrying the carbonyl groupis considered as the parent chain and the name is derived by replacing the terminal ‘e’ of the name of the corresponding alkane by letters ‘one’.
Ex: Propanone
2. In case of substituted ketones, theparent chain is numbered in such a way that the ketone group carbon gets the lowest number (but the numbering does not start from ketone group carbon – caron attached with a double bond to oxygen).
3. The position of carbonyl group and the substituents is indicated by numbers.
Ex: 3-methylbutan-2-one (indicated that there is methyl group at 3rd carbon and carbonyl group at 2nd carbon on butanone.
Compounds having both aldehyde and ketone groups.
For compounds having both aldehyde and ketone groups, the aldehyde group is considered as the principal functional group and ketonic group is regarded as substituent. It is named as prefix oxo- along with a number to indicate its position.
Ex: 2-Methyl-4-oxohexanal
Aromatic Ketones
Purely aromatic or mixed aromatics ketones are know by their common names.
Examples
Acetophenone – Methyl phenyl ketone
Propiophenone – Ethyl phenyl ketone
Benzophenone - Diphenyle ketone
IUPAC 1993 recommendation for 3 same functional groups
If an unbranched chain is directly bonded to more than two same functional groups, the organic compound is named as a derivative of parent alkane which does not include the carbon atoms of the functional groups. These compounds are named by use of suffix tricarboaldehyde (for three –CHO groups).
Ex: Butane-1,2,4-tricarbaldehyde
If three groups are not directly bonded to the unbranched carbon chain, the two like groups are considered in the parent chain and are named by using di before the name of the functional group. The third group forming the side chain is considered as a substituent group.
Ex: 3-Formylmethylhexane-1,6-dial (three –CHO groups are there. But at 1 and 6 they are directly bonded. At three there is a branching of the alkane chain and –CHO is attached to the methyl group of the branch).
Aldehydes and Ketones - Methods of Preparation
1. From alkenes
2. From alkynes
3 From alcohols
4. From alkyl halides
5. From Grignard reagent
6. From carboxylic acids
7.From Acid chlorides
8.From alkyl cyanides
1. From alkenes
Alkenes react with ozone to form ozonide which on subsequent cleavage with zinc dust and water gives aldehydes and ketones.
2. From alkynes
Hydration of alkynes in the presence of dilute sulphuric acid and HgSO4 as catalyst gives aldehydes and ketones.
Water adds to alkynes to form unstable enol intermediates which rearrange to form aldehydes or ketones.
Hydration of acetylene gives acetaldehyde.
Hydration of alkynes other than acetylene gives ketones.
3. By oxidation of alcohols:
a) Primary alcohols on oxidation by potassium dichromate and dilute sulphuric acid give corresponding aldehyde
Potassium dichromate and sulphuric combine to give (0) nascent oxygen. Nascent oxygen oxidizes CH3OH to HCHO by removing H2 from CH3OH.
Nascent oxygen removes H2 from C2H5OH to give CH3CHO.
b)Ketones: Secondary alcohols on oxidation by potassium dichromate and dilute sulphuric acid mixture give ketones.
Isopropyl alcohol gives acetone.
2-butanol gives ethyl methyl ketone on oxidation.
2. From alkynes
3 From alcohols
4. From alkyl halides
5. From Grignard reagent
6. From carboxylic acids
7.From Acid chlorides
8.From alkyl cyanides
1. From alkenes
Alkenes react with ozone to form ozonide which on subsequent cleavage with zinc dust and water gives aldehydes and ketones.
2. From alkynes
Hydration of alkynes in the presence of dilute sulphuric acid and HgSO4 as catalyst gives aldehydes and ketones.
Water adds to alkynes to form unstable enol intermediates which rearrange to form aldehydes or ketones.
Hydration of acetylene gives acetaldehyde.
Hydration of alkynes other than acetylene gives ketones.
3. By oxidation of alcohols:
a) Primary alcohols on oxidation by potassium dichromate and dilute sulphuric acid give corresponding aldehyde
Potassium dichromate and sulphuric combine to give (0) nascent oxygen. Nascent oxygen oxidizes CH3OH to HCHO by removing H2 from CH3OH.
Nascent oxygen removes H2 from C2H5OH to give CH3CHO.
b)Ketones: Secondary alcohols on oxidation by potassium dichromate and dilute sulphuric acid mixture give ketones.
Isopropyl alcohol gives acetone.
2-butanol gives ethyl methyl ketone on oxidation.
Aldehydes and Ketones - Chemical Properties
Reactions
Can studied with the following grouping
A. Nucleophilic addition reactions.
B. Nucleophilic addition reactions that involve elimination of water molecule
C. Oxidation reactions
D. Reduction reactions
E. Miscellaneous reactions
A. Nucleophilic addition reactions
1. Hydrogen cyanide: addition product is cyanohydrin
2. Sodium bisulphite: addition proudct is bisulphite adduct.
3. Grignard reagent: addition intermediate product, when hydrolysed gives alcohol
4. Alcohol: product geminal dialkoxy compounds.
B. Nucleophilic addition reactions that involve elimination of water molecule
Aldehydes and ketones react with a number of ammonia derivatives in weakly acidic medium to form compound containing carbon-nitrogen double bonds with the elimination of water molecule.
1. Addition of various ammonia derivatives
i) Hydroxylamine - product oxime
ii) Hydrazine - product hydrazone
iii) Phenylhydrazine - product phenylhydrazone
iv) 2, 4 dinitrophenyl hydrazine - product 2,4 dinitrophenyl hydrazone
v) Semicarbazide - product semicarbazone
2. Addition of Ammonia
product aldehyde-ammonia ducts
3. Primary amines
product azomethines also known as Schiff bases.
C. Oxidation reactions
i) Tollen's reagent - silver mirror test
ii) Fehling's solution - aldehydes give a red precipitate of cuprous oxide
iii) Benedict's solutin - similar to Fehling's solution
iv) Oxidation with sodium hypohalite - iodoform is the product
D. Reduction of aldehydes and ketones
1. Reduction to alcohols: aldehydes give primary alcohols. Ketones give secondary alcohols.
2. Reduction to hydrocarbons:
i) Reduction with zinc amalgam and con HCL
ii) Reductin with basic solution of hydrazine
iii) Reductioin with HI in the presence of red phosphorus
3. Reduction to pinacols
E. Miscellaneous reactions
1. Aldol condensation
2. Cross aldol condensation
3. Cannizaro's reaction
4. Halogenation
5. Action with Schiff's reagent
6. Polymerisation
7. Sunstitution reactions of benzene nucleus in aldehydes and ketones.
For more detailed coverage of some reactions
http://www.chem.uic.edu/web1/OCOL-II/WIN/CH19/F3.HTM
Can studied with the following grouping
A. Nucleophilic addition reactions.
B. Nucleophilic addition reactions that involve elimination of water molecule
C. Oxidation reactions
D. Reduction reactions
E. Miscellaneous reactions
A. Nucleophilic addition reactions
1. Hydrogen cyanide: addition product is cyanohydrin
2. Sodium bisulphite: addition proudct is bisulphite adduct.
3. Grignard reagent: addition intermediate product, when hydrolysed gives alcohol
4. Alcohol: product geminal dialkoxy compounds.
B. Nucleophilic addition reactions that involve elimination of water molecule
Aldehydes and ketones react with a number of ammonia derivatives in weakly acidic medium to form compound containing carbon-nitrogen double bonds with the elimination of water molecule.
1. Addition of various ammonia derivatives
i) Hydroxylamine - product oxime
ii) Hydrazine - product hydrazone
iii) Phenylhydrazine - product phenylhydrazone
iv) 2, 4 dinitrophenyl hydrazine - product 2,4 dinitrophenyl hydrazone
v) Semicarbazide - product semicarbazone
2. Addition of Ammonia
product aldehyde-ammonia ducts
3. Primary amines
product azomethines also known as Schiff bases.
C. Oxidation reactions
i) Tollen's reagent - silver mirror test
ii) Fehling's solution - aldehydes give a red precipitate of cuprous oxide
iii) Benedict's solutin - similar to Fehling's solution
iv) Oxidation with sodium hypohalite - iodoform is the product
D. Reduction of aldehydes and ketones
1. Reduction to alcohols: aldehydes give primary alcohols. Ketones give secondary alcohols.
2. Reduction to hydrocarbons:
i) Reduction with zinc amalgam and con HCL
ii) Reductin with basic solution of hydrazine
iii) Reductioin with HI in the presence of red phosphorus
3. Reduction to pinacols
E. Miscellaneous reactions
1. Aldol condensation
2. Cross aldol condensation
3. Cannizaro's reaction
4. Halogenation
5. Action with Schiff's reagent
6. Polymerisation
7. Sunstitution reactions of benzene nucleus in aldehydes and ketones.
For more detailed coverage of some reactions
http://www.chem.uic.edu/web1/OCOL-II/WIN/CH19/F3.HTM
Oxidation - Aldehydes - Ketones
Oxidation
Carbonyl groups in aldehydes and ketones may be oxidized to form
compounds at the next “oxidation level”, that of carboxylic acids.
• Alcohols are oxidized to aldehydes and ketones
(example: biological oxidation of ethanol to acetaldehyde)
• The carbonyl group may be further oxidized to carboxylic acids
Carbonyl groups in aldehydes and ketones may be oxidized to form
compounds at the next “oxidation level”, that of carboxylic acids.
• Alcohols are oxidized to aldehydes and ketones
(example: biological oxidation of ethanol to acetaldehyde)
• The carbonyl group may be further oxidized to carboxylic acids
Reduction - Aldehydes - Ketones
Oxidation of Aldehydes by Silver Oxide: Reaction of simple aldehydes with aqueous Ag2O in the presence of NH3 yields the corresponding carboxylic acid and metallic silver. The silver is generally deposited in a thin metallic layer which forms a reflective "mirror" on the inside surface of the reaction vessel. The formation of this mirror forms the basis of a qualitative test for aldehydes, called the Tollens Test.
Oxidation of Aldehydes to form Carboxylic Acids: Reaction of simple aldehydes with acidic MnO4-, or CrO3/H2SO4 yields the corresponding carboxylic acid. Aldehydes oxidize very easily and it is often difficult to prevent oxidation, even by atmospheric oxygen.
Oxidation of Ketones: Ketones are more resistant to oxidation, but can be cleaved with acidic MnO4- to yield carboxylic acids.
Oxidation of Aldehydes to form Carboxylic Acids: Reaction of simple aldehydes with acidic MnO4-, or CrO3/H2SO4 yields the corresponding carboxylic acid. Aldehydes oxidize very easily and it is often difficult to prevent oxidation, even by atmospheric oxygen.
Oxidation of Ketones: Ketones are more resistant to oxidation, but can be cleaved with acidic MnO4- to yield carboxylic acids.
oxime - Aldehydes - Ketones
Oximes can be synthesized by condensation of an aldehyde or a ketone with hydroxylamine.
The condensation of aldehydes with hydroxylamine gives aldoxime.
Ketoximes are produced from ketones and hydroxylamine.
Generally, oximes exist as colorless crystals and do not easily dissolve in water. Oximes can be used for the identification of ketone or aldehyde.
The condensation of aldehydes with hydroxylamine gives aldoxime.
Ketoximes are produced from ketones and hydroxylamine.
Generally, oximes exist as colorless crystals and do not easily dissolve in water. Oximes can be used for the identification of ketone or aldehyde.
hydrazone formation
Aldehydes and ketones also condense with other ammonia derivatives, such as hydroxylamine and hydrazines.
Generally these reactions are better than the analogous amine reactions (i.e. give superior yields).
Oximes are produced when hydroxylamines are reacted with aldehydes and ketones.
Hydrazones are produced through reaction of hydrazines with aldehydes and ketones.
Generally these reactions are better than the analogous amine reactions (i.e. give superior yields).
Oximes are produced when hydroxylamines are reacted with aldehydes and ketones.
Hydrazones are produced through reaction of hydrazines with aldehydes and ketones.
Aldehydes - Ketones aldol condensation
Aldehydes and ketones containing α-hydrogen (H-atoms attached to the C-atom adjacent to the carbonyl group)undergo condensation in the presence of dilute alkali.
In the resulting compound both aldehyde group and alcohol group are present.
acetaldehyde and acetone undergo aldol condensation.
Formaldehyde, banzaldehyde do not undergo aldol condensation.
Reagents : commonly a base such as NaOH or KOH is added to the aldehyde.
The reaction involves an enolate reacting with another molecule of the aldehyde.
Remember enolates are good nucleophiles and carbonyl C are electrophiles.
Since the pKa of an aldehyde is close to that of NaOH, both enolate and aldehyde are present.
The products of these reactions are β-hydroxyaldehydes or aldehyde-alcohols = aldols.
The simplest aldol reaction is the condensation of ethanal.
Step 1:
First, an acid-base reaction. Hydroxide functions as a base and removes the acidic α-hydrogen giving the reactive enolate.
Step 2:
The nucleophilic enolate attacks the aldehyde at the electrophilic carbonyl C in a nucleophilic addition type process giving an intermediate alkoxide.
Step 3:
An acid-base reaction. The alkoxide deprotonates a water molecule creating hydroxide and the β-hydroxyaldehydes or aldol product.
In the resulting compound both aldehyde group and alcohol group are present.
acetaldehyde and acetone undergo aldol condensation.
Formaldehyde, banzaldehyde do not undergo aldol condensation.
Reagents : commonly a base such as NaOH or KOH is added to the aldehyde.
The reaction involves an enolate reacting with another molecule of the aldehyde.
Remember enolates are good nucleophiles and carbonyl C are electrophiles.
Since the pKa of an aldehyde is close to that of NaOH, both enolate and aldehyde are present.
The products of these reactions are β-hydroxyaldehydes or aldehyde-alcohols = aldols.
The simplest aldol reaction is the condensation of ethanal.
Step 1:
First, an acid-base reaction. Hydroxide functions as a base and removes the acidic α-hydrogen giving the reactive enolate.
Step 2:
The nucleophilic enolate attacks the aldehyde at the electrophilic carbonyl C in a nucleophilic addition type process giving an intermediate alkoxide.
Step 3:
An acid-base reaction. The alkoxide deprotonates a water molecule creating hydroxide and the β-hydroxyaldehydes or aldol product.
Aldehydes - Ketones Perkin reaction
The Perkin reaction is a type of aldol condensation of aromatic aldehydes and the anhydride of an aliphatic acid in the presence of sodium salt of the same acid, to give on heating an α,β-unsaturated acid.
Reaction mechanism
The carboxylate anion abstracts a proton from the a-carbon of the anhydride to form carbanion I.
This carbanion undergoes nucleophilic addition to carbonyl carbon of the aldehyde.
The anion II so formed takes up a proton to form a hydroxy compound III which first undergoes dehydration as an anhydride before it is hydrolyzed to the α,β-unsaturated acid.
Reaction mechanism
The carboxylate anion abstracts a proton from the a-carbon of the anhydride to form carbanion I.
This carbanion undergoes nucleophilic addition to carbonyl carbon of the aldehyde.
The anion II so formed takes up a proton to form a hydroxy compound III which first undergoes dehydration as an anhydride before it is hydrolyzed to the α,β-unsaturated acid.
Aldehydes - Ketones Cannizzaro reaction
Aldehydes which do not have α-hydrogen atom react with concentrated sodium hydroxide (NaOH) or potassium hydroxide (KOH) in such a way that one molecule get oxidized to acid and the second molecule gets reduced to alcohol.
Note two molecules of aldehyde participates in the reaction.
This self oxidation-reduction under the influence of a base is known as the Cannizzaro's reaction.
Formaldehyde does not possess α-hydrogen atom and therefore undergoes Cannizzaro's reaction. Acetaldehyde does not give this reaction.
Formaldehyde (HCHO) two molecules + warm NaOH give Methanol (CH3OH) and Sodium Formate (CHOONa)
CH3OH is the reduction product HCHO becomes CH3OH (two hydrogen atoms are getting in).
CHOONa is the oxidation product. one 'H' has gone out and One 'O' came in along with Na.
Note two molecules of aldehyde participates in the reaction.
This self oxidation-reduction under the influence of a base is known as the Cannizzaro's reaction.
Formaldehyde does not possess α-hydrogen atom and therefore undergoes Cannizzaro's reaction. Acetaldehyde does not give this reaction.
Formaldehyde (HCHO) two molecules + warm NaOH give Methanol (CH3OH) and Sodium Formate (CHOONa)
CH3OH is the reduction product HCHO becomes CH3OH (two hydrogen atoms are getting in).
CHOONa is the oxidation product. one 'H' has gone out and One 'O' came in along with Na.
Aldehydes - Ketones -haloform reaction
When methyl ketones are treated with the halogen in basic solution, polyhalogenaton followed by cleavage of the methyl group occurs.
The products are the carboxylate and trihalomethane, otherwise known as haloform.
The reaction proceeds via successively faster halogenations at the α-position until the 3 H have been replaced.
The halogenations get faster since the halogen stablises the enolate negative charge and makes it easier to form.
Then a nucleophilic acyl substitution by hydroxide displaces the anion CX3(haloform) as a leaving group that rapidly protonates.
This reaction is often performed using iodine and as a chemical test for identifying methyl ketones. Iodoform(CI3) is yellow and precipitates under the reaction conditions.
Reaction mechanism
Step 1:
First, an acid-base reaction. Hydroxide functions as a base and removes the acidic α-hydrogen giving the enolate.
Step 2:
The nucleophilic enolate reacts with the iodine giving the halogenated ketone and an iodide ion.
Step 3:
Steps 1 and 2 repeat twice more yielding the trihalogenated ketone.
Step 4:
The hydroxide now reacts as a nucleophile at the electrophilic carbonyl carbon, with the C=O becoming a C-O single bond and the oxygen is now anionic.
Step 5:
Reform the favourable C=O and displace a leaving group, the trihalomethyl system which is stabilised by the 3 halogens. This gives the carboxylic acid.
Step 6:
An acid-base reaction. The trihalomethyl anion is protonated by the carboxylic acid, giving the carboxylate and the haloform (trihalomethane).
The products are the carboxylate and trihalomethane, otherwise known as haloform.
The reaction proceeds via successively faster halogenations at the α-position until the 3 H have been replaced.
The halogenations get faster since the halogen stablises the enolate negative charge and makes it easier to form.
Then a nucleophilic acyl substitution by hydroxide displaces the anion CX3(haloform) as a leaving group that rapidly protonates.
This reaction is often performed using iodine and as a chemical test for identifying methyl ketones. Iodoform(CI3) is yellow and precipitates under the reaction conditions.
Reaction mechanism
Step 1:
First, an acid-base reaction. Hydroxide functions as a base and removes the acidic α-hydrogen giving the enolate.
Step 2:
The nucleophilic enolate reacts with the iodine giving the halogenated ketone and an iodide ion.
Step 3:
Steps 1 and 2 repeat twice more yielding the trihalogenated ketone.
Step 4:
The hydroxide now reacts as a nucleophile at the electrophilic carbonyl carbon, with the C=O becoming a C-O single bond and the oxygen is now anionic.
Step 5:
Reform the favourable C=O and displace a leaving group, the trihalomethyl system which is stabilised by the 3 halogens. This gives the carboxylic acid.
Step 6:
An acid-base reaction. The trihalomethyl anion is protonated by the carboxylic acid, giving the carboxylate and the haloform (trihalomethane).
Aldehydes - Ketones-nucleophilic addition reactions
Addition Using Grignard Reagents•
Primary, secondary and tertiary alcohols may be formed in the reactions of
aldehydes or ketones with Grignard reagents.
Primary, secondary and tertiary alcohols may be formed in the reactions of
aldehydes or ketones with Grignard reagents.
Carboxylic acids - introduction
1. Carboxylic acids are the compound containing carboxyl group in their molecules.
-C with a double bond with oxygen and single bond with OH
2. These acides can be aliphatic or aromatic.
aliphatic acids:
Formic acid HCOOH
Acetic acid CH-3COOH
Isobutyric acid (Branched)
aromatic acids
Bezoic acid : H in benzene substituted by COOH
m-Nitrobenzoic acid: One more H substituted by NO-2
o-Toluic acid (o refers to ortho) Benzoic acid with one more H substituted by CH-3
Both aliphatic and aromatic carboxylic acids are further classified as mono, di, tricarboxylic acids depending upon the number of carboxylic groups present in their molecules.
Some dicarboxylic acids
Oxalic acid COOOH-COOH
Malonic acd CH2(COOH)2
Succinic acid (CH2COOH)2
Phthalic acid is an aromatic dicarboxylic acid Ar(COOH)2. 2nd COOH is in ortho position
Phthalic acid come in the amines, as primary amines are prepared from Phthalimide using Gabriel's phthalimide synthesis.
Isophthalic acid (2nd COOH in meta position)
Terephtalic acid (2nd COOH in para position)
Nomenclature
According to IUPAC system, the name of the monocarboxylic acid is derived by changing the final 'e' from the name of the corresponding hydrocarbon with 'oic' and adding the word acid.
Formic acid - Methanoic acid
Acetic acid - Ethanoic acid
n-Butyric acid - Butanoic acid
Isobutyric acid - 2-Mehtylpropanoic acid
Dicarboxylic acids
Oxalic acid - Ethanedioic acid
Malonic acid - Propanedioic acid
-C with a double bond with oxygen and single bond with OH
2. These acides can be aliphatic or aromatic.
aliphatic acids:
Formic acid HCOOH
Acetic acid CH-3COOH
Isobutyric acid (Branched)
aromatic acids
Bezoic acid : H in benzene substituted by COOH
m-Nitrobenzoic acid: One more H substituted by NO-2
o-Toluic acid (o refers to ortho) Benzoic acid with one more H substituted by CH-3
Both aliphatic and aromatic carboxylic acids are further classified as mono, di, tricarboxylic acids depending upon the number of carboxylic groups present in their molecules.
Some dicarboxylic acids
Oxalic acid COOOH-COOH
Malonic acd CH2(COOH)2
Succinic acid (CH2COOH)2
Phthalic acid is an aromatic dicarboxylic acid Ar(COOH)2. 2nd COOH is in ortho position
Phthalic acid come in the amines, as primary amines are prepared from Phthalimide using Gabriel's phthalimide synthesis.
Isophthalic acid (2nd COOH in meta position)
Terephtalic acid (2nd COOH in para position)
Nomenclature
According to IUPAC system, the name of the monocarboxylic acid is derived by changing the final 'e' from the name of the corresponding hydrocarbon with 'oic' and adding the word acid.
Formic acid - Methanoic acid
Acetic acid - Ethanoic acid
n-Butyric acid - Butanoic acid
Isobutyric acid - 2-Mehtylpropanoic acid
Dicarboxylic acids
Oxalic acid - Ethanedioic acid
Malonic acid - Propanedioic acid
Methods of Preparation of Monocarboxylic Acids
Methods of Preparation of Monocarboxylic Acids:
1. From oxidation of primary alcohols
Primary alcohols are oxidized with potassium permanganate or potassium dichromate to aldehydes which on further oxidation give carboxylic acids.
2. By oxidation of aldehydes and ketones.
This method is already part method 1.
Aldehydes are easily oxidised to carboxylic acids even with mild oxidising agents like Tollen's reagent.
3. From hydrolysis of nitriles and cyanides
the nitriles are hydrolysed in dilute acqueous acidic or alkaline medium.
4. From Grignard reagents
The reaction is carried out by bubbling CO2 through th etheral solution of suitable Grignard reagent.
5. By hydrolysis of esters
Hydrolysis of esters with mineral acids or alkalines gives carboxylic acids
6. Carboxylaiton of alkenes
Heating alkenes with CO and steam under pressure with phospoiric acid at 673 K. This reaction is called Koch reaction.
7. From trihalogen derivatives of hydrocarbons
Hydroysis of 1,1,1,-trihalogen derivatives of alkanes with acqueous KOH.
8. Preparation of aromatic acids from alkyl benzenes
the alkyl side cahin of benzene ring can be easily oxidized to carboxylic group iwth alkalines KMnO4, chromic anhydride or conc. HNO3.
1. From oxidation of primary alcohols
Primary alcohols are oxidized with potassium permanganate or potassium dichromate to aldehydes which on further oxidation give carboxylic acids.
2. By oxidation of aldehydes and ketones.
This method is already part method 1.
Aldehydes are easily oxidised to carboxylic acids even with mild oxidising agents like Tollen's reagent.
3. From hydrolysis of nitriles and cyanides
the nitriles are hydrolysed in dilute acqueous acidic or alkaline medium.
4. From Grignard reagents
The reaction is carried out by bubbling CO2 through th etheral solution of suitable Grignard reagent.
5. By hydrolysis of esters
Hydrolysis of esters with mineral acids or alkalines gives carboxylic acids
6. Carboxylaiton of alkenes
Heating alkenes with CO and steam under pressure with phospoiric acid at 673 K. This reaction is called Koch reaction.
7. From trihalogen derivatives of hydrocarbons
Hydroysis of 1,1,1,-trihalogen derivatives of alkanes with acqueous KOH.
8. Preparation of aromatic acids from alkyl benzenes
the alkyl side cahin of benzene ring can be easily oxidized to carboxylic group iwth alkalines KMnO4, chromic anhydride or conc. HNO3.
Carboxylic acids - Characteristic reactions
Grouping of the reactions
A. Reactions due to hydrogen atom of carboxyl group
B. Reactions due to OH part of carboxyl group
C. Reactions due to carboxyl group
D. Reactions due to alkyl group and benzene ring
A. Reactions due to hydrogen atom of carboxyl group
1. Acidic character
a. Action with blue litmus
all carboxylic acids turn blue litmus red.
b. Reaction with metals: liberation of hydrogen
Carboxylic acids react with active metals such as Na, K, Ca, Mg, Zn, etc., to form their salts with the liberation of hydrogen.
c. Action with alkalies: formation of salts
Carboxylic acids neutralize alkalies forming salts and water.
d. Action with carbonates and bicarbonates: evolving carbon dioxide
Carboxylic acids decompose carbonates and bicarbonates evolving carbon dioxide with brisk effervescence.
Mechanism of acidic character
In the COOH group due to resonance in the OH, O acquires some positive charge the electron pair of OH is drawn towards O. This displacement of electrons causes the release of a proton and a carboxylate ion, RCOO- is formed. This is the reason for acidic character of carboxylic acids.
The strength of acids can be expressed in terms of dissociation constant Ka or Ph number of PKa number which is pKa = -log Ka
A stronger acid will have a higher Ka value but smaller PKa value.
Effects of substituents on acidic strength of acids
Electron releasing substituents: Alkyl is an electron releasing group. If the H atom of formic acid (HCOOH) is replaced by CH3 group to form acetic acid (CH3COOH) the alkyl group will tend to increase the electron density on the oxygen atom of the O-H bond. This increase will make removal H+ ion difficult in comparison to formic acid.
Acetic acid is a weaker acid in comparison to formic acid.
The electron release effect is called +I effect. As +I effect increases, acidic strength will go down. As more alkyl groups are there +I effect increases
CH3
Therefore acidic property is stronger or more for CH3COOH.
Acidic strength is in the following order
acidic strength of HCOOH>CH3COOH>CH3CH2COOH>(CH3)2CHCOOH
Electron withdrawing substituents: Substituents like halogens tend to withdraw the electron charge. Halogens are electron attracting atoms(-I inductive effect). They withdraw the electrons from the carbon to which they are attached and this effect is transmitted throught the chain. The increases positive charge on O atom in the O-H bond and dissociation of H+ ion or proton takes place more easily.
Hence chloroacetic acid is stronger acid than acetic acid.
B. Reactions due to OH part of carboxyl group
The -OH group of carboxylic acids can be replaced by a number of groups such as, -Cl, -NH2, OR, -OOCR’ to form chlorides, amides, esters ad anhydrides.
Formation of acid chlorides
Acetic acid + PCl5 Acetyl chloride + POCL3 + HCl
Formation of esters
When carboxylic acids are heated with alcohols in the presence of concentrated sulphuric acid, esters are formed.
Formation of amides
Carboxylic acids react with ammonia to form ammonium salts.
Acetic acid + Ammonia Ammonium acetate
Ammonium acetate on heating gives acetamide plus water.
Formation of acid anhydrides
Carboxylic acids on heating in the presence of a strong dehydrating agent such as phosphorous pentoxide form acid anhydrides.
C. Reactions due to carboxyl group
Decarboxylation:
Salts of carboxylic acids get decarboxylated – lose carbon dioxide in some reactions.
a. Sodium or potassium salts of carboxylic acids on heating with soda lime give alkanes.
b. Electrolysis of acqueous solutions of sodium or potassium salts of carboxylic acids gives alkanes due to decarboxylation.
c. When calcium salts of monocarboxylic acids (fatty acids) are heated aldehydes or ketones are formed.
Reduction
a. Partial reduction: Carboxylic acids on reduction with lithium aluminium hydride or with hydrogen in the presence of copper chromite are reduced to alcohols.
b. Complete reduction to alkanes: Carboxylic acids on reduction with HI and red P give alkanes.
Action of bromine on silver salt of acid:
The silver saltsof the carboxylic acid on treatment with Br2 in the presence of CCl4 give alkyl halides having one carbon atom less than the parent acid.
This reaction is called Hunsdiecker reaction.
D. Reactions due to alkyl group and benzene ring
Halogenation
Carboxylic acids react with chlorine on bromine in the presence of a small amount of phosphorus to give halogenated compounds. The reaction is called Hell Volhard-Zelinksy reaction.
Ring substitution in aromatic acids:
In substitution reactions with aromatic carboxylic acids, carboxyl group is an electron withdrawing group and therefore it favours meta position for the substituent.
Hence benzoinc acid + bromine gives 3-Bromobenzoic acid
A. Reactions due to hydrogen atom of carboxyl group
B. Reactions due to OH part of carboxyl group
C. Reactions due to carboxyl group
D. Reactions due to alkyl group and benzene ring
A. Reactions due to hydrogen atom of carboxyl group
1. Acidic character
a. Action with blue litmus
all carboxylic acids turn blue litmus red.
b. Reaction with metals: liberation of hydrogen
Carboxylic acids react with active metals such as Na, K, Ca, Mg, Zn, etc., to form their salts with the liberation of hydrogen.
c. Action with alkalies: formation of salts
Carboxylic acids neutralize alkalies forming salts and water.
d. Action with carbonates and bicarbonates: evolving carbon dioxide
Carboxylic acids decompose carbonates and bicarbonates evolving carbon dioxide with brisk effervescence.
Mechanism of acidic character
In the COOH group due to resonance in the OH, O acquires some positive charge the electron pair of OH is drawn towards O. This displacement of electrons causes the release of a proton and a carboxylate ion, RCOO- is formed. This is the reason for acidic character of carboxylic acids.
The strength of acids can be expressed in terms of dissociation constant Ka or Ph number of PKa number which is pKa = -log Ka
A stronger acid will have a higher Ka value but smaller PKa value.
Effects of substituents on acidic strength of acids
Electron releasing substituents: Alkyl is an electron releasing group. If the H atom of formic acid (HCOOH) is replaced by CH3 group to form acetic acid (CH3COOH) the alkyl group will tend to increase the electron density on the oxygen atom of the O-H bond. This increase will make removal H+ ion difficult in comparison to formic acid.
Acetic acid is a weaker acid in comparison to formic acid.
The electron release effect is called +I effect. As +I effect increases, acidic strength will go down. As more alkyl groups are there +I effect increases
CH3
Therefore acidic property is stronger or more for CH3COOH.
Acidic strength is in the following order
acidic strength of HCOOH>CH3COOH>CH3CH2COOH>(CH3)2CHCOOH
Electron withdrawing substituents: Substituents like halogens tend to withdraw the electron charge. Halogens are electron attracting atoms(-I inductive effect). They withdraw the electrons from the carbon to which they are attached and this effect is transmitted throught the chain. The increases positive charge on O atom in the O-H bond and dissociation of H+ ion or proton takes place more easily.
Hence chloroacetic acid is stronger acid than acetic acid.
B. Reactions due to OH part of carboxyl group
The -OH group of carboxylic acids can be replaced by a number of groups such as, -Cl, -NH2, OR, -OOCR’ to form chlorides, amides, esters ad anhydrides.
Formation of acid chlorides
Acetic acid + PCl5 Acetyl chloride + POCL3 + HCl
Formation of esters
When carboxylic acids are heated with alcohols in the presence of concentrated sulphuric acid, esters are formed.
Formation of amides
Carboxylic acids react with ammonia to form ammonium salts.
Acetic acid + Ammonia Ammonium acetate
Ammonium acetate on heating gives acetamide plus water.
Formation of acid anhydrides
Carboxylic acids on heating in the presence of a strong dehydrating agent such as phosphorous pentoxide form acid anhydrides.
C. Reactions due to carboxyl group
Decarboxylation:
Salts of carboxylic acids get decarboxylated – lose carbon dioxide in some reactions.
a. Sodium or potassium salts of carboxylic acids on heating with soda lime give alkanes.
b. Electrolysis of acqueous solutions of sodium or potassium salts of carboxylic acids gives alkanes due to decarboxylation.
c. When calcium salts of monocarboxylic acids (fatty acids) are heated aldehydes or ketones are formed.
Reduction
a. Partial reduction: Carboxylic acids on reduction with lithium aluminium hydride or with hydrogen in the presence of copper chromite are reduced to alcohols.
b. Complete reduction to alkanes: Carboxylic acids on reduction with HI and red P give alkanes.
Action of bromine on silver salt of acid:
The silver saltsof the carboxylic acid on treatment with Br2 in the presence of CCl4 give alkyl halides having one carbon atom less than the parent acid.
This reaction is called Hunsdiecker reaction.
D. Reactions due to alkyl group and benzene ring
Halogenation
Carboxylic acids react with chlorine on bromine in the presence of a small amount of phosphorus to give halogenated compounds. The reaction is called Hell Volhard-Zelinksy reaction.
Ring substitution in aromatic acids:
In substitution reactions with aromatic carboxylic acids, carboxyl group is an electron withdrawing group and therefore it favours meta position for the substituent.
Hence benzoinc acid + bromine gives 3-Bromobenzoic acid
Formation of esters
Esters are compounds which are formed when the hydroxy hydrogen atom in oxygen acids is replaced by an alkyl group. The acid may be organic or inorganic.
Esters of organic acid:
These are compounds formed by replacing the hydrogen atom of the carboxyl group by an alkyl group.
In -COOH of carboxylic acids H is replaced an alkyl group.
It may be represented as R-COOH-R'.
Acetic acid + Ethanol ---> Ethyl acetate (Ethyl ethanoate) + water
Ethyl acetate (Ethyl ethanoate) is ester CH3COOC2H5
When a carboxylic acid is heated with an alcohol in presence of dehydrating agent like concentrated sulphuric acid , it gives an ester.
Esters of organic acid:
These are compounds formed by replacing the hydrogen atom of the carboxyl group by an alkyl group.
In -COOH of carboxylic acids H is replaced an alkyl group.
It may be represented as R-COOH-R'.
Acetic acid + Ethanol ---> Ethyl acetate (Ethyl ethanoate) + water
Ethyl acetate (Ethyl ethanoate) is ester CH3COOC2H5
When a carboxylic acid is heated with an alcohol in presence of dehydrating agent like concentrated sulphuric acid , it gives an ester.
carboxylic acid chlorides
Carboxylic acids can be converted into acid chlorides by treatment with phosphorous chlorides (PCl5, Pcl3) or thionyl chloride (SOcl2) in pyridine.
Acetic acid + Phosphorous Pentachloride = Acetyl chloride + POCl3 + HCL
acetic acid + PCl3 = Acetyl chloride + HePO3
acetic acid + thionyl chloride = acetyl chloride + sulphur dioxide + HCl
From benzoic acid we get benzoyl chloride
Acetic acid + Phosphorous Pentachloride = Acetyl chloride + POCl3 + HCL
acetic acid + PCl3 = Acetyl chloride + HePO3
acetic acid + thionyl chloride = acetyl chloride + sulphur dioxide + HCl
From benzoic acid we get benzoyl chloride
Ch.28 Carboxylic Acid - Ester Hydrolysis
Ester hydrolysis
Hydrolysis of Esters
Esters are hydrolysed water and the process is accelerated by dilute mineral acids (HCL or H2SO4) or alkalies.
Ethyl acetate + water gives Acetic acid + Ethyl alcohol (in the presence of dilute mineral acid)
Ethyl acetate + Sodium hydroxide (alkali) Sodium acetate + Ethyl alcohol
Acidic hydrolysis is reversible.
Alkaline hydrolysis is irreversible because resonance stabilized carboxylate (acetate ion is formed and it has very little tendency to react with an alcohol.
Hydrolysis of esters by alkalies is known as saponification. Saponification leads to the formation of soaps. It is a very rapid reaction as alkali acts as catalyst and also as a reactant.
Mechanism of alkaline hydrolysis of esters.
Step I. the nucleophile, OH ¯ ion from the alkali attacks the carboxyl carbon to form an intermediate
Step II the intermediate, then loses a molecule of ethoxide ion to form acetic acid .
Step III. Ethoxide ion then removes a proton from acetic acid and thus acetate ion is formed.
Step IV. This acetate ion combines with Na+ to form Sodium acetate.
Hydrolysis of Esters
Esters are hydrolysed water and the process is accelerated by dilute mineral acids (HCL or H2SO4) or alkalies.
Ethyl acetate + water gives Acetic acid + Ethyl alcohol (in the presence of dilute mineral acid)
Ethyl acetate + Sodium hydroxide (alkali) Sodium acetate + Ethyl alcohol
Acidic hydrolysis is reversible.
Alkaline hydrolysis is irreversible because resonance stabilized carboxylate (acetate ion is formed and it has very little tendency to react with an alcohol.
Hydrolysis of esters by alkalies is known as saponification. Saponification leads to the formation of soaps. It is a very rapid reaction as alkali acts as catalyst and also as a reactant.
Mechanism of alkaline hydrolysis of esters.
Step I. the nucleophile, OH ¯ ion from the alkali attacks the carboxyl carbon to form an intermediate
Step II the intermediate, then loses a molecule of ethoxide ion to form acetic acid .
Step III. Ethoxide ion then removes a proton from acetic acid and thus acetate ion is formed.
Step IV. This acetate ion combines with Na+ to form Sodium acetate.
IIT JEE Revision - Ch.29 Phenols - Core Points
JEE syllabus
Phenols:
Preparation, Physical and Chemical properties
specially highlighted topics
Acidity,
electrophilic substitution reactions (halogenation, nitration and sulphonation);
Reimer-Tieman reaction,
Kolbe reaction.
----------
Phenols are aromatic hydroxy compounds. In phenols, one or more hydroxyl group is directly attached to the aromatic (benzene) nucleus.
If OH group is not directly attached to be carbon atom in the benzene ring, but present in the molecule as a part of the alkyl side chain group, then the compound is not termed as phenol.It is called aromatic alcohol because it resembles aliphatic alcohols in its characteristics.
By decarboxylation of sodium salt of salicyclic acid
Fusion of sodium salicylate with soda lime (NaOH and CaO mixture).
sodium phenoxide is formed. This on acidification gives phenol.
State and smell: Phenols are colourless crystalline solids or liquids. They have characteristic phenolic odours.
Boiling points: Higher than the boiling points of the aromatic hydrocarbons of comparable molecular masses.
Bromination
Action of Bromine water on phenol: When phenol is treated with bromine water, it gets decolourised giving a white precipitate of 2,4,6, tribromophenol.
Action of Bromine in CS-2 on phenol:o-Bromophenol + p-Bromophenol mixture is obtained. p-Bromophenol is the major product.
Nitration
Action of dilute nitirc acid on phenol: a mixture of o-nitrophenol and p-nitrophenol is formed.
Action of conc. nitric acid in the presence of conc. sulphuric acid on phenol: 2,4,6-trinitrophenol is formed. This is picric acid.
Sulphonation
Action of conc. sulphuric acid at different temperatures on phenol:
Pheno reacts with conc. sulphuric acid to form a mixture of o-, and p-phenol sulphonic acid.
At low temperature about 288 to 293 K, o-phenol sulphonic acid is the main product formed.
At high temperature about 373 K, p-phenol sulphonic acid is the main product formed.
Acidity of Phenols
Phenols are weakly acidic in nature (Ka = 10^-10).
They turn blue litmus read and react with alkali metals and alkalies to form their salts.
The acidic character of phenol is due to polar OH bond.
Kolbe's reaction
When sodium phenoxide is heated with carbon dioxide at about 400K and under 4 ot 7 atmospheric pressure, sodium salicylate is formed as a major product. This on acidification gives salicylic acid. A small amount of para isomer is also obtained and if the temperature is allowed to rise above 410 K, the para isomer dominates.
Reimer-Tiemann reaction
When phenol is treated with choloroform and aqueous sodium hydroxide at 340 K follwoed by hydrolysis, an aldehydic group, -CHO group is introduced in the ring at a position ortho to the phenol group (OH group).
Ortho hydroxy benzaldehyde or salicylaldehyde is formed as the product of the reaction.
In addition, small amount of p-salicylaldehyde is also formed
In place of chloroform, carbon tetrachloride can be used. In this case o-salicylic acid is formed as the major product.
Phenols:
Preparation, Physical and Chemical properties
specially highlighted topics
Acidity,
electrophilic substitution reactions (halogenation, nitration and sulphonation);
Reimer-Tieman reaction,
Kolbe reaction.
----------
Phenols are aromatic hydroxy compounds. In phenols, one or more hydroxyl group is directly attached to the aromatic (benzene) nucleus.
If OH group is not directly attached to be carbon atom in the benzene ring, but present in the molecule as a part of the alkyl side chain group, then the compound is not termed as phenol.It is called aromatic alcohol because it resembles aliphatic alcohols in its characteristics.
By decarboxylation of sodium salt of salicyclic acid
Fusion of sodium salicylate with soda lime (NaOH and CaO mixture).
sodium phenoxide is formed. This on acidification gives phenol.
State and smell: Phenols are colourless crystalline solids or liquids. They have characteristic phenolic odours.
Boiling points: Higher than the boiling points of the aromatic hydrocarbons of comparable molecular masses.
Bromination
Action of Bromine water on phenol: When phenol is treated with bromine water, it gets decolourised giving a white precipitate of 2,4,6, tribromophenol.
Action of Bromine in CS-2 on phenol:o-Bromophenol + p-Bromophenol mixture is obtained. p-Bromophenol is the major product.
Nitration
Action of dilute nitirc acid on phenol: a mixture of o-nitrophenol and p-nitrophenol is formed.
Action of conc. nitric acid in the presence of conc. sulphuric acid on phenol: 2,4,6-trinitrophenol is formed. This is picric acid.
Sulphonation
Action of conc. sulphuric acid at different temperatures on phenol:
Pheno reacts with conc. sulphuric acid to form a mixture of o-, and p-phenol sulphonic acid.
At low temperature about 288 to 293 K, o-phenol sulphonic acid is the main product formed.
At high temperature about 373 K, p-phenol sulphonic acid is the main product formed.
Acidity of Phenols
Phenols are weakly acidic in nature (Ka = 10^-10).
They turn blue litmus read and react with alkali metals and alkalies to form their salts.
The acidic character of phenol is due to polar OH bond.
Kolbe's reaction
When sodium phenoxide is heated with carbon dioxide at about 400K and under 4 ot 7 atmospheric pressure, sodium salicylate is formed as a major product. This on acidification gives salicylic acid. A small amount of para isomer is also obtained and if the temperature is allowed to rise above 410 K, the para isomer dominates.
Reimer-Tiemann reaction
When phenol is treated with choloroform and aqueous sodium hydroxide at 340 K follwoed by hydrolysis, an aldehydic group, -CHO group is introduced in the ring at a position ortho to the phenol group (OH group).
Ortho hydroxy benzaldehyde or salicylaldehyde is formed as the product of the reaction.
In addition, small amount of p-salicylaldehyde is also formed
In place of chloroform, carbon tetrachloride can be used. In this case o-salicylic acid is formed as the major product.
Phenols - Introduction, Nomenclature
Phenols are aromatic hydroxy compounds. In phenols, one or more hydroxyl group is directly attached to the aromatic (benzene) nucleus.
If OH group is not directly attached to be carbon atom in the benzene ring, but present in the molecule as a part of the alkyl side chain group, then the compound is not termed as phenol.It is called aromatic alcohol because it resembles aliphatic alcohols in its characteristics.
If OH group is not directly attached to be carbon atom in the benzene ring, but present in the molecule as a part of the alkyl side chain group, then the compound is not termed as phenol.It is called aromatic alcohol because it resembles aliphatic alcohols in its characteristics.
Phenols - Preparation
1. Alkali fusion of sodium benzene sulphonate
NaOH is fused with sodium benzene sulphonate at 573 - 623 K. sodium phenoxide is formed. This on acidification gives phenol.
2. From diazonium salts
An acqueous solution of benzene diazonium salt on warming gives phenol
3. By decarboxylation of sodium salt of salicyclic acid
Fusion of sodium salicylate with soda lime (NaOH and CaO mixture).
sodium phenoxide is formed. This on acidification gives phenol.
4. From Grignard reagent
When oxygen gas is bubbled through an ethereal solution of phenyl magnesium bromide (Grignard reagent RMgX), it forms an oxy compound which upon hydrolysis with dilute mineral acid gives phenol.
Commercial Preparation of Phenols
1. From chlorobenzene (Dow's Process)
Chlorobenzene is heated with 10% acqueous sodium hydroxide solution at about 623 K under 200 atmospheres and in the presence of copper salt acting as catalyst to form sodium phenoxide.
The sodium salt when treated with dilute HCl, gives phenol.
2. From cumene
Air or oxygen is passed through a suspension of cumene in acqueous sodium carbonate solution in presence of cobalt or manganese naphthenate catalyst. The oxidation product is cumene hydroperoxide.
The hydroperoxide is then decomposed by hot dilute sulphuric acid when phenol is formed with liberation of acetone.
3. From Benzene (Raschig's method)
Vapours of HCl are passed over benzene at 500 K in the presence of copper chloride and excess of air to form chlorobenzene.
Steam is then passed through chlorobenzene at 800 K in the presence of silica as catalyst to give phenol.
4. Phenol prepared using benzene and H2SO4
Benzene is heated with excess of concentrated sulphuric acid at about 388 K to give benzene sulphonic acid.
It is neutralized with sodium hydroxide solution, when sodium benzene sulphonate is obtained.
Dry sodium benzene sulphonate is next fused with excess of caustic soda at about 573 K when it yields sodium phenate (or sodium phenoxide).
Sodium phenate is decomposed by dilute sulphuric acid to give phenol.
***In many methods sodium phenoxide is formed first and from sodium phenoxide, phenol is obtained.
NaOH is fused with sodium benzene sulphonate at 573 - 623 K. sodium phenoxide is formed. This on acidification gives phenol.
2. From diazonium salts
An acqueous solution of benzene diazonium salt on warming gives phenol
3. By decarboxylation of sodium salt of salicyclic acid
Fusion of sodium salicylate with soda lime (NaOH and CaO mixture).
sodium phenoxide is formed. This on acidification gives phenol.
4. From Grignard reagent
When oxygen gas is bubbled through an ethereal solution of phenyl magnesium bromide (Grignard reagent RMgX), it forms an oxy compound which upon hydrolysis with dilute mineral acid gives phenol.
Commercial Preparation of Phenols
1. From chlorobenzene (Dow's Process)
Chlorobenzene is heated with 10% acqueous sodium hydroxide solution at about 623 K under 200 atmospheres and in the presence of copper salt acting as catalyst to form sodium phenoxide.
The sodium salt when treated with dilute HCl, gives phenol.
2. From cumene
Air or oxygen is passed through a suspension of cumene in acqueous sodium carbonate solution in presence of cobalt or manganese naphthenate catalyst. The oxidation product is cumene hydroperoxide.
The hydroperoxide is then decomposed by hot dilute sulphuric acid when phenol is formed with liberation of acetone.
3. From Benzene (Raschig's method)
Vapours of HCl are passed over benzene at 500 K in the presence of copper chloride and excess of air to form chlorobenzene.
Steam is then passed through chlorobenzene at 800 K in the presence of silica as catalyst to give phenol.
4. Phenol prepared using benzene and H2SO4
Benzene is heated with excess of concentrated sulphuric acid at about 388 K to give benzene sulphonic acid.
It is neutralized with sodium hydroxide solution, when sodium benzene sulphonate is obtained.
Dry sodium benzene sulphonate is next fused with excess of caustic soda at about 573 K when it yields sodium phenate (or sodium phenoxide).
Sodium phenate is decomposed by dilute sulphuric acid to give phenol.
***In many methods sodium phenoxide is formed first and from sodium phenoxide, phenol is obtained.
Phenols - Physical properties
State and smell: Phenols are colourless crystalline solids or liquids. They have characteristic phenolic odours.
Boiling points: Higher than the boiling points of the aromatic hydrocarbons of comparable molecular masses.
Boiling points: Higher than the boiling points of the aromatic hydrocarbons of comparable molecular masses.
Phenols - Chemical Properties
Can be classified into three groups
A. Reactions of phenolic group (-OH group)
B. Reactions of benzene ring
C. Special reactions
A. Reactions of phenolic group (_OH group)
1.Acidic character:
They turn blue litmus red and react with alkali metals and alkalies to form their salts.
Phenol is weaker acid than carboxylic acid and stronger acid compared to alcohols.
2. Action with zinc dust
When heated with zinc dust, phenol is reduced to benzene.
3. Action with ammonia
Phenol reacts with ammonia in the presenceof anhydrous zinc chloride to give aniline.
4. Action with acid chlorides and acid anhydrides
Esters are formed.
5. Action with benzyl chloride
Phneol benzoate is formed. The reaction occurs in the presence of aqueous NaOH.
Reaction is named Schotten Baumann reaction
B. Reactions of benzene ring (Substitution)
Phenols undergo electrophilic aromatic substitution reactions. OH group is an activating group. Therefore the reactions with phenol occur at a faster rate than reaction with benzene. OH group directs the substituents to ortho and para positions.
Substituents
1a. Bromine Br in ortho and para positions 2,4,6-tribromophenol
1b. If the reaction is carried out in CS2 or CCl4, a mixture of ortho and para bromophenol is obtained.
2a. NO2 - Reaction of phenol with concentrated HNO3 in the presence of H2SO4 gives 2,4,6-trinitrophenol.
2,4,6-trinitrophenol is also termed picric acid.
2b. With dilute nitric acid phenol reacts at low temperature (293K) and gives a mixture of ortho and para nitrophenol.
3. NO – reaction with nitrous acid (NaNO2 + HCL) at low temperature (280 K) gives p-nitrosophenol (p indicates that NO is in para position to OH)). This reaction is called nitrosation.
4. SO3H – Phenol reacts with concentrated sulphuric acid to form a mixture of 0- and p-phenol sulphonic acid.
5. CH3 – When phenol is heated with alkyl halides in the presence of anhydrous chloride, CH3 becomes a substituent. The phenol with CH3 as a substituent is termed Cresol. O-cresol and p-cresol are formed. The reaction is called Friedel Craft reaction.
Special reactions of Phenol
1. Kolbe's reaction:
It is a reaction of sodium phenoxide.
When sodium phenoxide is heated with carbon dioxide at about 400 K and under 4 to 7 atm, sodium salicylate is formed as a major product. This on acidification gives salicylic acid.
2. Reimer-Tiemann reaction:
When phenol is refluxed with chloroform in the presence of acqueous sodium hydroxide at 340 K followed by hydrolysis, an aldehydic group (HC=O) gets introduced in the ring at a position ortho to the phenolic group. So ortho hydroxy bezaldehyde is formed. It is also called salicylaldehyde.
3. Coupling reaction
In the alkaline medium, an ice cold solution of phenol combines with an ice cold solution of benzene diazonium chloride to form azo dye.
4. Reaction with pthalic anhydride
Phenol reacts with phthalic anhydride in the presence of conc. H2So4 to give phenolphthalein.
5. Condensation with formaldehyde
Phenol condenses with formaldehyde in the presence of dil. Acid or alkali as catalyst to give a polymer called bakelite.
6. Hydrogenation
Phenol can be converted to cyclohexagonal in the presence of nickel catalyst at 430 K.
7. Oxidation
On exposure to air or chromic acid, phenol undergoes oxidation to p-benzoquinone. It is a pink coloured compound.
8. Reaction with ferric chloride
Phenols react with neutral ferric chloride to form coloured water soluble complex compounds.
9. Libermann's test
On warming with conc. H2SO4 and sodium nitrite, phenols give red or brown colouration. The colour changes to blue or green by the addition of aqueous NaOH.
A. Reactions of phenolic group (-OH group)
B. Reactions of benzene ring
C. Special reactions
A. Reactions of phenolic group (_OH group)
1.Acidic character:
They turn blue litmus red and react with alkali metals and alkalies to form their salts.
Phenol is weaker acid than carboxylic acid and stronger acid compared to alcohols.
2. Action with zinc dust
When heated with zinc dust, phenol is reduced to benzene.
3. Action with ammonia
Phenol reacts with ammonia in the presenceof anhydrous zinc chloride to give aniline.
4. Action with acid chlorides and acid anhydrides
Esters are formed.
5. Action with benzyl chloride
Phneol benzoate is formed. The reaction occurs in the presence of aqueous NaOH.
Reaction is named Schotten Baumann reaction
B. Reactions of benzene ring (Substitution)
Phenols undergo electrophilic aromatic substitution reactions. OH group is an activating group. Therefore the reactions with phenol occur at a faster rate than reaction with benzene. OH group directs the substituents to ortho and para positions.
Substituents
1a. Bromine Br in ortho and para positions 2,4,6-tribromophenol
1b. If the reaction is carried out in CS2 or CCl4, a mixture of ortho and para bromophenol is obtained.
2a. NO2 - Reaction of phenol with concentrated HNO3 in the presence of H2SO4 gives 2,4,6-trinitrophenol.
2,4,6-trinitrophenol is also termed picric acid.
2b. With dilute nitric acid phenol reacts at low temperature (293K) and gives a mixture of ortho and para nitrophenol.
3. NO – reaction with nitrous acid (NaNO2 + HCL) at low temperature (280 K) gives p-nitrosophenol (p indicates that NO is in para position to OH)). This reaction is called nitrosation.
4. SO3H – Phenol reacts with concentrated sulphuric acid to form a mixture of 0- and p-phenol sulphonic acid.
5. CH3 – When phenol is heated with alkyl halides in the presence of anhydrous chloride, CH3 becomes a substituent. The phenol with CH3 as a substituent is termed Cresol. O-cresol and p-cresol are formed. The reaction is called Friedel Craft reaction.
Special reactions of Phenol
1. Kolbe's reaction:
It is a reaction of sodium phenoxide.
When sodium phenoxide is heated with carbon dioxide at about 400 K and under 4 to 7 atm, sodium salicylate is formed as a major product. This on acidification gives salicylic acid.
2. Reimer-Tiemann reaction:
When phenol is refluxed with chloroform in the presence of acqueous sodium hydroxide at 340 K followed by hydrolysis, an aldehydic group (HC=O) gets introduced in the ring at a position ortho to the phenolic group. So ortho hydroxy bezaldehyde is formed. It is also called salicylaldehyde.
3. Coupling reaction
In the alkaline medium, an ice cold solution of phenol combines with an ice cold solution of benzene diazonium chloride to form azo dye.
4. Reaction with pthalic anhydride
Phenol reacts with phthalic anhydride in the presence of conc. H2So4 to give phenolphthalein.
5. Condensation with formaldehyde
Phenol condenses with formaldehyde in the presence of dil. Acid or alkali as catalyst to give a polymer called bakelite.
6. Hydrogenation
Phenol can be converted to cyclohexagonal in the presence of nickel catalyst at 430 K.
7. Oxidation
On exposure to air or chromic acid, phenol undergoes oxidation to p-benzoquinone. It is a pink coloured compound.
8. Reaction with ferric chloride
Phenols react with neutral ferric chloride to form coloured water soluble complex compounds.
9. Libermann's test
On warming with conc. H2SO4 and sodium nitrite, phenols give red or brown colouration. The colour changes to blue or green by the addition of aqueous NaOH.
Nitration of Phenol
Nitration
Action of dilute nitirc acid on phenol: a mixture of o-nitrophenol and p-nitrophenol is formed.
Action of conc. nitric acid in the presence of conc. sulphuric acid on phenol: 2,4,6-trinitrophenol is formed. This is picric acid.
Action of dilute nitirc acid on phenol: a mixture of o-nitrophenol and p-nitrophenol is formed.
Action of conc. nitric acid in the presence of conc. sulphuric acid on phenol: 2,4,6-trinitrophenol is formed. This is picric acid.
Sulphonation of Phenol
Sulphonation
Action of conc. sulphuric acid at different temperatures on phenol:
Pheno reacts with conc. sulphuric acid to form a mixture of o-, and p-phenol sulphonic acid.
At low temperature about 288 to 293 K, o-phenol sulphonic acid is the main product formed.
At high temperature about 373 K, p-phenol sulphonic acid is the main product formed.
Action of conc. sulphuric acid at different temperatures on phenol:
Pheno reacts with conc. sulphuric acid to form a mixture of o-, and p-phenol sulphonic acid.
At low temperature about 288 to 293 K, o-phenol sulphonic acid is the main product formed.
At high temperature about 373 K, p-phenol sulphonic acid is the main product formed.
Acidity of Phenols
Acidity of Phenols
Phenols are weakly acidic in nature (Ka = 10^-10).
They turn blue litmus read and react with alkali metals and alkalies to form their salts.
The acidic character of phenol is due to polar OH bond.
Phenols are weakly acidic in nature (Ka = 10^-10).
They turn blue litmus read and react with alkali metals and alkalies to form their salts.
The acidic character of phenol is due to polar OH bond.
Reimer-Tiemann reaction - Phenols
Reimer-Tiemann reaction
When phenol is treated with choloroform and aqueous sodium hydroxide at 340 K followed by hydrolysis, an aldehydic group, -CHO group is introduced in the ring at a position ortho to the phenol group (OH group).
Ortho hydroxy benzaldehyde or salicylaldehyde is formed as the product of the reaction.
In addition, small amount of p-salicylaldehyde is also formed
In place of chloroform, carbon tetrachloride can be used. I this case o-salicylic acid is formed as the major product.
When phenol is treated with choloroform and aqueous sodium hydroxide at 340 K followed by hydrolysis, an aldehydic group, -CHO group is introduced in the ring at a position ortho to the phenol group (OH group).
Ortho hydroxy benzaldehyde or salicylaldehyde is formed as the product of the reaction.
In addition, small amount of p-salicylaldehyde is also formed
In place of chloroform, carbon tetrachloride can be used. I this case o-salicylic acid is formed as the major product.
Kolbe reaction Phenols
Kolbe's reaction
When sodium phenoxide is heated with carbon dioxide at about 400K and under 4 to 7 atmospheric pressure, sodium salicylate is formed as a major product. This on acidification gives salicylic acid. A small amount of para isomer is also obtained and if the temperature is allowed to rise above 410 K, the para isomer dominates.
When sodium phenoxide is heated with carbon dioxide at about 400K and under 4 to 7 atmospheric pressure, sodium salicylate is formed as a major product. This on acidification gives salicylic acid. A small amount of para isomer is also obtained and if the temperature is allowed to rise above 410 K, the para isomer dominates.
Boron
IIT
JEE
Boron (B)
Z = 5, 1s²2s²2px¹
Boron belongs to 13th group.
Method of obtaining Boron
By the reduction of boric oxide by an electropositive metal like magnesium.
JEE
Boron (B)
Z = 5, 1s²2s²2px¹
Boron belongs to 13th group.
Method of obtaining Boron
By the reduction of boric oxide by an electropositive metal like magnesium.
Silicon
silicon (Si) -
Atomic Number is 14. 1s²2s²2p^63s²3p²
Method of obtaining Silicon: Heating finely divided silica with magnesium powder.
Atomic Number is 14. 1s²2s²2p^63s²3p²
Method of obtaining Silicon: Heating finely divided silica with magnesium powder.
Revison - Halogens
Halogens
Flourine (F), Chlorine (Cl), Bromine (Br), Iodine (I).
Chlorine is yellow green gas
Bromine is reddish brown liquid
Iodine is steel grey solid
Flourine (F), Chlorine (Cl), Bromine (Br), Iodine (I).
Chlorine is yellow green gas
Bromine is reddish brown liquid
Iodine is steel grey solid
Revision - Allotropes of Carbon
IIT JEE
Allotrope
• Allotropes are elements that can exist in two or more different physical forms
• Diamond, graphite and buckminster fullerine are allotropes of carbon.
• The allotropes of carbon are all the element carbon. The type of carbon is determined from the bonding that occurs.
The carbon atoms in graphite are arranged in flat sheets that slide easily over each other, while the atoms in diamond are bonded in a complex, honeycombed structure that makes the solid much harder.
Allotrope
• Allotropes are elements that can exist in two or more different physical forms
• Diamond, graphite and buckminster fullerine are allotropes of carbon.
• The allotropes of carbon are all the element carbon. The type of carbon is determined from the bonding that occurs.
The carbon atoms in graphite are arranged in flat sheets that slide easily over each other, while the atoms in diamond are bonded in a complex, honeycombed structure that makes the solid much harder.
phosphorous allotropes
Phosphorous occurs in three forms--white, red, and black.
White phosphorous is poisonous and very reactive.
Red phosphorous is not poisonous and it is only moderately reactive.
Black phosphorous is nearly inert.
White phosphorous is poisonous and very reactive.
Red phosphorous is not poisonous and it is only moderately reactive.
Black phosphorous is nearly inert.
Revision - Sodium Compounds
Sodium Oxide
Sodium oxide has formula Na2O.
It is also called sodium(I) oxide, disodium oxide, sodium monoxide, and soda.
Sodium peroxide
A nearly white compound (Na 2 O 2 ), having vigorous oxidizing properties, and used in bleaching mechanical paper pulps and as a final stage in the bleaching of chemical paper pulps in some multi-stage bleaching sequences.
Sodium hydroxide
sodium hydroxide chemical compound, NaOH, is a white crystalline substance that readily absorbs carbon dioxide and moisture from the air.
Sodium carbonate
Sodium carbonate exists as anhydrous (Na2CO3) and also as hydrated salt. The decahydrated salt (Na2CO3.10H2O) is known as washing soda while the anhydrous salt is called soda ash.
Sodium Bicarbonate NaHCO-3
Sodium Bicarbonate, commonly called baking soda, is a white odourless, crystalline solid, completely soluble in water but slightly soluble in ethanol. It is the mildest of all sodium alkalis.
Sodium chloride
Sodium chloride (NaCl) or common salt is an ionic crystal consisting of equal numbers of sodium and chlorine atoms and is an essential component in the human diet, being found in blood sweat and tears.
Sodium sulphate
FORMULA Na2SO4
Sodium sulfate is a white, orthorhombic crystalline solid at room temperatures ( a monoclinic structure at > 100 C, a hexagonal structure at > 250C).
Sodium oxide has formula Na2O.
It is also called sodium(I) oxide, disodium oxide, sodium monoxide, and soda.
Sodium peroxide
A nearly white compound (Na 2 O 2 ), having vigorous oxidizing properties, and used in bleaching mechanical paper pulps and as a final stage in the bleaching of chemical paper pulps in some multi-stage bleaching sequences.
Sodium hydroxide
sodium hydroxide chemical compound, NaOH, is a white crystalline substance that readily absorbs carbon dioxide and moisture from the air.
Sodium carbonate
Sodium carbonate exists as anhydrous (Na2CO3) and also as hydrated salt. The decahydrated salt (Na2CO3.10H2O) is known as washing soda while the anhydrous salt is called soda ash.
Sodium Bicarbonate NaHCO-3
Sodium Bicarbonate, commonly called baking soda, is a white odourless, crystalline solid, completely soluble in water but slightly soluble in ethanol. It is the mildest of all sodium alkalis.
Sodium chloride
Sodium chloride (NaCl) or common salt is an ionic crystal consisting of equal numbers of sodium and chlorine atoms and is an essential component in the human diet, being found in blood sweat and tears.
Sodium sulphate
FORMULA Na2SO4
Sodium sulfate is a white, orthorhombic crystalline solid at room temperatures ( a monoclinic structure at > 100 C, a hexagonal structure at > 250C).
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