Question

The increasing order of the rate of nucleophilic addition to compounds A - D is:

(A) HCHO

(B) CH₃COCH₃

(C) PhCOCH₃ 

(D) PhCOPh

Options

• A < B < C < D

• D < B < C < A

• D < C < B < A

• C < D < B < A

Answer 1

D < C < B < A

Explanation:

Aldehydes are more reactive than Ketones towards nucleophillic addition reactions (a) is aldehyde and othercompond are ketones, so HCHO is more reactive than B,C and D.

Aliphatic ketones are more reactive than aromatic ketones

This is due to the following two reasons.

1. Steric reasons: Bulky phenyl group in ketones hinders than approach of nucleophile to carbonyl carbon.
2. Electronic reasons: Due to resonance aromactic Ketones are less a reactive than aliphatic ketones, so B is more reactive than C and D.

Nucleophilic addition ∝ \[\frac{1}{\text{No. of resonating structures}}\]

So, C is more reactive than D.