Tuesday, February 5, 2008

IIt JEE Revision Ch.26 Alkyl and Aryl Halides - Core Points

syllabus


METHODS OF PREPARATION
PHYSICAL PROPERTIES
CHEMICAL REACTIONS
charateristic reactions

Specially highlighed topics

Rearrangement reactions of alkyl carbocation,
Grignard reactions,
Nucleophilic substitution reactions;
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1. When hydrogen atom or atoms of alkanes are replaced by the corresponding number of halogen atoms, the compounds are called halogen derivatives of alkanes.



2. 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)

3. The only methyl halide which is a liquid is iodomethane.chloroethane is a gas.

4. 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.

5. Nucleophilic substitution in tertiary halogenoalkanes - The nucleophilic substitution reaction - an SN1 reaction (1 denotes 1st order)

6.

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