(a) Write the chemical reaction involved in Wolff-Kishner reduction. (b) Arrange the following in the increasing order of their reactivity towards nucleophilic addition reaction: C6H5COCH3, CH3CHO, CH3COCH3. (c) Why carboxylic acid does not give reactions of carbonyl group?

(a) In Wolff-Kishner reduction, the carbonyl group of aldehydes and ketones is converted into a methylene group. Aldehydes or ketones are heated with hydrazine and KOH or potassium tert-butoxide in ethylene glycol to form alkanes.
R−C(O)−R'(i) H2N−NH2, H2O → (ii) KOH/ethylene glycol, Δ R−CH2−R' + N2
(b) C6H5COCH3 < CH3COCH3 < CH3CHO
In general, aldehydes are more reactive than ketones. The aromatic aldehydes and ketones are less reactive than aliphatic counterparts.
(c) The lone pair of electrons on the O atom of the -OH group of carboxylic acid is in resonance with the carbonyl group. Hence, the carbonyl carbon of carboxylic acid is less electrophilic than the carbonyl carbon of aldehydes or ketones. Hence, carboxylic acid does not give reactions of the carbonyl group.
(d) DIBAL-H reduces nitriles to aldehydes.
CH3CH2CH=CH−CH2CN 1. (i-Bu)2AlH → 2. H2O CH3CH2CH=CH−CH2CHO
(e) B forms a yellow precipitate of iodoform. Hence, B is a methyl ketone as it undergoes the haloform reaction. Thus, B is acetone (CH3COCH3). The isomer A does not form any precipitate. Hence, it is not a methyl ketone. Hence A is propanal (CH3CH2CHO)