The relative reactivities of acyl compounds towards nucleophilic substitution are in the order of
- Acid anhydride > Amide > Ester > Acyl chloride
- Acyl chloride > Ester > Acid anhydride > Amide
- Acyl chloride > Acid anhydride > Ester > Amide
- Ester > Acyl chloride > Amide > Acid anhydride.
Answer
(3) Acyl chloride > Acid anhydride > Ester > Amide
Solution
Nucleophilic acyl substitution is easier when the leaving group is a weaker base (better leaving group) and when the group gives less resonance donation to the carbonyl carbon.
Leaving groups: Cl- (acyl chloride) > RCOO- (acid anhydride) > RO- (ester) > NH2- (amide)
Resonance donation to C=O is largest from -NH2, so amides are the least reactive.
Acyl chloride > Acid anhydride > Ester > Amide
Answer: (3)