Learning CHEMISTRY for IIT JEE: September 2007

Thursday, September 27, 2007

One question for day in each subject

Visit www.iit-jee-nrao.blogspot.com

Started on 25/9/07

Thursday, September 20, 2007

IIT JEE orkut community

Join

http://www.orkut.com/Community.aspx?cmm=39291603
IIT-JEE-ACADEMY

if you are a student, parent, family member, faculty, author, book publisher

Wednesday, September 19, 2007

Answers and Questions

A set of questions on varius chapters of organic chemistry are posted in

www.iit-jee-chemistry-ps.blogspot.com

I am presently posting answers to those questions in

www.iit-jee-chemistry-aps.blogspot.com

Tuesday, September 18, 2007

Question Bank for Organic chemistry

I have completed posting first round of question bank for various chapters of organic chemistry.
I developed simple questions which will be of help in solving more complicated objective questions. I plan to frame complicated questions using answers to these simple questions some time later.I included some of the questions from previous JEE exams in these questions.

I shall start posting answers to these questions from October 2nd week. I shall be on tour for a fortnight starting next week.

http://iit-jee-chemistry-ps.blogspot.com/

Monday, September 17, 2007

Study Guide TMH JEE Ch.28 Carboxylic Acid

JEE syllabus

Carboxylic acids:
Preparation, properties
Characteristic reactions
formation of esters,
acid chlorides and amides,
ester hydrolysis;

----------
Main Topics Covered in the TMH Book

METHODS OF PREPARATION
PHYSICAL PROPERTIES
CHEMICAL REACTIONS
FUNCTIONAL DERIVATIVES OF 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

The carboxyl group is made up of carbonyl C with double bond with oxygen, and hydroxyl group OH. The carboxyl is formed carbo + oxyl.

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

Dicarboxyic acids

Oxalic acid
Malonic acid
Succinic acid
Phthalic acid - It is an aromatic carboxylic acid

In the nomenclature, in common system, position of the sustituents is indicated by the greek letter alpha, beta, gamma and delta.

the carbon atom adjacent ot the carboxyl carbon is assigned the letter α, thenext carbon on chain is beta an so on.

According to the IUPAC system, the name of the acid is derived from the corresponding alkane by replacing the terminal 'e' with the '-oic' and adding the word acid.

The position of the substituents is indicated by the following rules:
1. The longest chain containing the carboxylic group (-COOH) is selected.
2. The carbon chain is numbered form the carboxylic acid group. The carbon of carboxyl group is always given number one.
3. The position of the substituents is indicated by the number.

Methods of Preparation of Monocarboxylic Acids:
1. From oxidation of primary alcohols
2. By oxidation of aldehydes and ketones.
3. By Hydrolysis of cyanides (or Nitriles)
4. By Grignard reaction
5. By hydrolysis of esters
6. By carboxylation of alkenes
7. From trihalogen derivatives of hydrocarbons
8. Aromatic acids from alkyl benzenes

Physical properties

State
B.P.
M.P.
Solubility

Reactions of carboxylic Acids

covered under the following heads

A. reactions due to hydrogen atom of carboxyl group
B. reactions due to OH 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 Properties

B. reactions due to OH carboxyl group
1. Formation of an acid anhydride
2. Formation of Esters (specially mentined in JEE syllabus)
3. Formation of amides (specially mentined in JEE syllabus)
4. Formation of acid chlorides (specially mentined in JEE syllabus)

C. reactions due to carboxyl group
1. Decarboxylation
2. Reduction
3. Action of bromine on silver salt of the acid
D. reactions due to alkyl group and benzene ring.
1. Halogenation
2. Ring substitution in aromatic acids

Ester hydrolysis (specially mentined in JEE syllabus) (from jauhar's book section on esters page 806)
---------
web sites
www.goiit.com/chapters/tutorial/chemistry/carboxyllic_acid.htm

Sunday, September 9, 2007

TMH JEE Book Chapters

Physical Chemistry

1. The Concept of Atoms and Molecules
2. Gaseous, Liquid and Solid States
3. Atomic Structure
4. Periodicity of Properties of Elements
5. Bonding and Molecular Structure
6. Energetics
7. Chemical Equilibrium
8. Electrochemistry
9. Solutions
10. Chemical Kinetics
11. Surface Chemistry
12. Nucluear Chemistry

Inorganic Chemistry
13. Non-Metals
14 Compounds of Metals
15 Compound of Nonmetals
16 Transition Elements
17 Ores/Minerals and Extractive Metallurgy
18. Exercises in Inorganic Chemistry

Organic Chemistry

19. Hybridization, Isomerism
20. Inductive and Resonance Effects
21. Alkanes
22. Alkenes
23. Alkynes
24. Benzene
25. Alcohols
26. Alkyl and Aryl Halides
27. Aldehydes and Ketones
28. Carboxylic Acids
29. Phenols
30. Amines
31. Carbohydrates
32. Aminoacids and Peptides
33. Polymers
34. Exercises in Organic Chemistry

IIT JEE Chemistry Blog Map

Sunday, September 2, 2007

My questions and answers on orkut - isomers

Narayana Rao

Isomer of C four H eight
A book mentioned that one of the isomers of C four H eight (butene) is cyclobutane. How is it possible?

Jüri
Cyclobutane consists of 4 -CH2- units in corners of a rectangle, the corners are linked along sides of the retangle. Isomers needn't to have the same structure. Isomers are all compounds which have the same brief formula.

Narayana Rao
thank you.

Saturday, September 1, 2007

TMH-JEE-chemistry-Study Guide - ch 23 Alkynes Part 2

Chemical Properties

The alkynes have at least one triple bond in them, therefore, they are quite reactive chemically.

They readily take part in addition reactions and can also be easily oxidized.

I. Addition reactions (specially given in jee syllabus)

1. Addition of Hydrogen

If the triple bond is not present at the end of the chain of the molecule (it is not a terminal alkyne), its reduction (addition of hydrogen) produces either a cis alkene or a trans alkene depending upon the choice of reducing agent.

2. Addition of halogens

chlorine and bromine add on alkali

3. Addition of hydrogen halides

This addition takes place in accordance with Markonikov's rule(do you remember the rule?).
Peroxides have the same effect on addition of the HBr to acetylenes (alkynes) as they have on alkenes (do you remember the effect?).

4. Addition of water (hydration of alkynes) (specially given in jee syllabus)
In the presence of acid (H2SO4) and HgSO-4, a molecule of water adds to the triple bond at 348K. The catalyst in this reaction is HgSO4 (Mercuric sulphate). The final products of this reaction are carbonyl compounds aldehydes and ketones.

Initially enol is formed which is raidly converted into an equilibrium mixture containing keto form in excess. Enol is so called because it contains 'ene' (double bond) and an alcoholic group (ol).

Examples:
Addition of water to Ethyne or acytelene: Acetylene is passed into water (at about 330K) containing 60% H2SO4 and about 1% mercuric sulphate (HgSO4) as a catalyst, acetaldehyde is formed.

In the first step 'ethenol' is formed and in the second step the rearrangement of it takes place and its isomer 'acetaldehyde' is formed.

The conversion of enol form into keto form is termed tautomerism

5. Addition of hypohalous acid (HOX)

Alkynes react with two molecules of hypohalous acids in two stages.
For example take ethyne or acytelene and HOCl.
In the first stage HO gets added to one carbon and Cl adds to the other carbon.
In the second stage one more HOCl gets added to the intermediate product which has a double bond. The addition now follows markonikov's rule. OH gets added to HC-OH and Cl gets added to CH-Cl. Two OHs create instability and H2O molecule gets removed.
An aldehyde 2,2-Dichloroethanal (Dichloroacetaldehyde) is formed.

6. Addition of H2SO4 (Ref: Standard XI Chemistry by Khan et al, Uttam Prakashan)
Acetylene adds two molecules of concentrated H2SO4 in two stages and forms ethylidene hydrogen sulphate as the final product.

In the first stage Vinylhydrogen sulphate H2C=CH-OSO3H is formed. (H gets added to one CH and OSO3H gets added to the other CH).
The addition of second molecule follows markownikov's rule. H gets added to CH2 and OSO3 gets added to the other carbon. Thus two functional groups OSO3H gets added to one carbon.
The final product is Ethylidine hydrogen sulphate.

II. Oxidation

a) Combustion

b) Oxidation with alkaline potassium permanganate

c) Ozonolysis

Alkynes react with ozone to form ozonides. These ozonides on decomposition with water in the presence of zinc give diketones(two carbonyl groups).

Ethyne gives glyoxal on reacting with ozone. Glyoxal also have two carbonyl groups.

III. Polymerization

a) Acytylene dimerizes (two molecules come together as one molecule) in the presence of cuprous chloride and ammonium chloride to give vinyl acetylene which on reacting with HCl gives chloroprene.

The later polymerizes to give neoprene - a synthetic rubber.

b) Cyclic polymerization

This takes place when alkyne is passed through red hot iron tube at 400 degress celsius.

Occurs in two stages. Acetylene becomes mesitylene.

IV. Isomerization

1-alkyne gets converted to 2-alkyne and vice versa.

V. Formation of metal acetylides (specially given in jee syllabus)

Acytelene reacts with Na and LI liberating H-2 gas and forming metal acetylide. Therefore acetylene has chemical behaviour similar to acids.

Heavy metal ions mainly, Ag+ and Cu+ react with acetylinic hydrogen (hydrogen atom in acetylene) to form insoluble acetylides.

VI. Reaction with Grignard reagent or alkyl-lithium

The acytylinic hydrogen on reacting with R'MgBr or R'Li produces the alkane R'H and metal acetylide

Acidic property of acetylene (specially given in jee syllabus)

Acetylene and other terminal alkynes (1-alkynes) are weakly acidic in character.
They react with strong bases like NaNH2 ( sodium in liquid ammonia) to form sodium acetylide derivatives known as acetylides or alkynides.

Acetylides react with alkyl halides to give higher alkynes.

Explanation for the acidic character of alkynes

the acidic character of 1-alkynes can be explained on the basis of sp hybridisation state of the carbon atoms in alkynes. In sp hybridisation, s-character is 50% and due to this large s-character, the electons in sp hybrid orbitals are held more tightly by thenucleus and areq uite electronegative. Consequently the eletron pair of H-C≡C bond gets displaced more towards the carbon atom and helps in release of H+ ion.

In the case of nonterminal alkynes, hydrogen atom is not attached directly to the triple bonded carbon atom and hence it is not released easily.

Alkynes are weakly acidic but alkenes and alkanes do not show acidic behaviour.

acidic charater
HC≡HC > CH2=CH2 > CH3-CH3

The relative acidity of acetylene is more than that of ammonia but less than that of water.

Dissolving Metal Reduction of Alkynes (specially given in jee syllabus)

Reaction Type: Addition

Summary

Alkynes can be reduced to trans-alkenes using Na in NH3 (l)
This reaction is stereospecific giving only the trans-alkene via an anti addition.
Note that the stereochemistry of this reaction complements that of catalytic hydrogenation (syn)
The reaction proceeds via single electron transfer from the Na with H coming from the NH3
These reaction conditions do not reduce alkenes, hence the product is the alkene.

MECHANISM FOR THE REDUCTION OF ALKYNES WITH Na / NH3
Step 1:
Sodium transfers an electron to the alkyne giving a radical anion.
Step 2:
The radical anion removes a proton from the ammonia in an acid / base reaction.
Step 3:
A second atom of sodium transfers another electron to the alkyne giving an anion.
Step 4:
The anion removes a proton from the ammonia in an acid / base reaction.
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Source for reduction
http://library.tedankara.k12.tr/carey/ch9-7.html
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Study Guide TMH JEE Ch.23 Alkynes

JEE syllabus

Preparation, properties and reactions of alkynes:

Physical properties of alkynes (boiling points, density and dipole moments);
Acidity of alkynes;
Acid catalysed hydration of alkynes (excluding the stereochemistry of addition and elimination);

Reduction of alkynes;
Preparation of alkynes by elimination reactions;
Addition reactions of alkynes;
Metal acetylides.
----------------------

Main Topics Covered in the TMH Book

METHODS OF PREPARATION
CHEMICAL PROPERTIES

--------------

From X class book

General formula: C(n)H(2n-2)
================================================
Structural--------------Common------------IUPAC
Formula:----------------name--------------name
------------------------------------------------
C two H two ---------Acetylene------------------Ethyne
C three H four------ Methyl acetylene-----------Propyne
C four H six *------ ethyl acetylene------------1-Butyne
--------------------------------------(Triple bond is the
--------------------------------------first carbon bond)
C four H six*--------Dimethyl acetylene---2-Butyne
---------------------------------------(Triple bond is the
----------------------------------------2nd carbon bond)
=========================================================

Preparation of Ethyne:

1. Calcium Carbide + Water = Ethyne + Calcium Hydroxide

(Cold water is added dropwise through a thistle funnel into conical flask containing calcium carbide at room temperature)

2. By dehydrohalogenation reaction

1,2 dibromoethane + KOH(alcoholic) = Ethyne + KBR + water (equation not balanced)

3. Methane on thermal decomposition by pyrolysis gives Ethyne + Hydrogen at around 1500 degree Celsius in an electric arc.
-------------------
Methods of Preparation of Alkynes; From TMH Book

1. Dehydrohalogenation of vicinal dihalides (came in X class book).

What are vicinal dihalides?

term used to describe the location of two identical chemical groups or atoms which are bonded to adjacent carbon atoms.

The process takes place in two stages.

In stage I KOH(alc) reacts with vicinal dihalide and vinylic halide is formed.

what is vinylic halide?

A vinyl halide in chemistry is any alkene with at least one halide substituent bonded directly on one of the unsaturated carbons.

This first stage requires mild conditions.

second stage: Vinyl halide is unreactive and hence vigorous conditions are required and a strong base NaNH two is used in the reaction to produce the corresponding alkyne.

2. Reaction of metal acetalides with primary alkyl halides. This method can be used to generate large alkyne from the smaller one.

Secondary and tertiary halides cannot be used because eliminatin is the predominant reaction which results in the formation of alkenes.

3. Hydrolysis of CaC two and Mg two C three.

Calcium carbide in reaction with water gives ethyne and calcium hydroxide.(came in X class)
Magnesium carbide in reaction water gives propyne and magnesium hydroxide.

4. Kolbe's Electrolytic Method:
The electrolysis of an acqueous solution of potassium salt of an unsaturated dicarboxylic acid forms alkyne

what is a dicarboxylic acid?

Dicarboxylic acids are organic compounds that are substituted with two carboxylic acid functional groups. In molecular formulae for dicarboxylic acids, these groups are often written as HOOC-R-COOH, where R is usually an alkyl, alkenyl, or akynyl group. Dicarboxylic acids can be used to prepare copolymers such as nylon and polyethylene terephthalate.

In general, dicarboxylic acids show the same chemical behaviour and reactivity as monocarboxylic acids. The ionization of the second carboxyl group occurs less readily than the first one. This is because more energy is required to separate a positive hydrogen ion from the doubly charged anion than from the single charged anion.

A mnemonic to aid in remembering the order of the common nomenclature for the first six dicarboxylic acids is "Oh my, such great apple pie!" (oxalic, malonic, succinic, glutaric, adipic, pimelic).

When one of the carboxy groups is replaced with an aldehyde group, the resulting structure is called a "aldehydic acid".

5. Dehalogenation of vic-tetrahalogen compounds

Tetrahalogenated alkane in reaction with zinc with ethyl alcohol as catalyst gives alkyne and zinc halide.
-------------------

From the Book by Madan and Bisht: preparation of Acetylene or Ethyne

1. By the action of Alcoholic Potash on Ethylene Bromide

BrH two C - CH two Br + 2KOH = C Two H Two + @KBr + 2 H two O

At the end of first state vinyl bromide is formed.

2. By heating tetra-bromoethane with Zinc

C-two H-two Br-four +2Zn = C-two H-two + 2ZnBr-two

3. By the electrolysis of Acqueous solution of Potassium salts of maleic acid (Kolbe's method)

4. By the action of water on calcium carbide (already covered earlier)

5. By heating Iodoform with silver powder

2HCI-three + 6Ag = C-twoH-two + 6AgI

6. By partial oxidation of Methane

2CH-four + 3[O] = C-twoHtwo + 3H-two O

7. By direct synthesis of carbon and hydrogen (Berthelot's synthesis)

2C + H-two = C-twoH-two

------------------------------------------------------------------

From Jauhar's book

1. Action of water on calcium carbide
2. Dehydrohalogenation of vicinal dihalides
3. Action of zinc on tetrahalogen derivatives of alkanes
4. From acetylene
5. By electrolysis of aqueous solution of potassium salt of fumaric acid
6. Synthesis of carbon and hydrogen

Industrial preparation
Ethyne is prepared on an industrial scale by treating calcium carbide with water.
-------------------------
Physical properties

State; first three members are gases at room temperature. thenext eight are liquids while the higher ones are solids.

Solubulity: are mostly insoluble in water nbut are soluble in organic solvents such as petroleum, ether, carbon tetrachlorde. benzene etc.

M.P. and B.P.

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Simple questions on methods of preparing alkynes are given in practice questions for review of concepts of this topic.
http://iit-jee-chemistry-ps.blogspot.com/
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