Question

Give reasons for the following.

1. Carboxylic acids do not give characteristic reactions of carboxyl group 

2. Treatment of benzaldehyde with HCN gives a mixture of two isomers which cannot be separated even by careful fractional distillation. 

3. Sodium bisuiphite is used for the purification of aldehydes and ketones.

Answer 1

1. It is due to reasonance

2. It is because we get two optical isomers which have same physical properties, therefore, cannot be separated by fractional distillation.

3. Aldehydes and ketones form addition compounds with NaHSO whereas any impurities do not. On hydrolysis, we get pure aldehydes and ketones back again.