Ncert Exercises & Solutions

Arrange the following alkyl halides in decreasing order of the rate of $β$ -elimination reaction with alcoholic KOH.

1. A > B > C

2. C > B > A

3. B > C > A

4. A > C > B

Hint: Stability of alkene decide the rate of reaction

Alkyl halides on heating with alcoholic potash eliminates one molecule of HX to form an alkene. Hydrogen is eliminated from

β

-carbon atom, thus this reaction is know as

β

-elimination reaction. Stability of product that is alkene determines rate of reaction.

The

3 °

alkyl halide will give more substituted alkene and it is most stable alkene. The

1 °

alkyl halide give less substituted alkene has it is least reactive. The order is as follows:

i.e.,

3 ° > 2 ° > 1 ° or A > C > B