Question

The relative reactivities of acyl compounds towards nucleophilic substitution are in the order of

• A. acyl chloride > acid anhydride > ester > amide
• B. ester > acyl chloride > amide > acid anhydride
• C. acid anhydride > amide > ester > acyl chloride
• D. acyl chloride > ester > acid anhydride > amide

Answer 1

The Correct Option is A

 To determine the order of reactivity of acyl compounds towards nucleophilic substitution, we need to consider the stability and reactivity of the leaving groups in these compounds. The basic principle is that the better the leaving group, the more reactive the compound will be towards nucleophilic substitution.

1. Acyl Chloride: Acyl chlorides have chloride ions as their leaving group, which is a very good leaving group due to its ability to stabilize electrons through resonance and its weak nucleophilicity. Therefore, acyl chlorides are highly reactive.
2. Acid Anhydride: Acid anhydrides have a carboxylate ion as their leaving group, which is less stable than a chloride ion but still quite favorable. Hence, acid anhydrides are moderately reactive.
3. Ester: Esters have an alkoxide ion as a leaving group, which is poorer compared to chloride and carboxylate ions, making esters less reactive than acyl chlorides and acid anhydrides.
4. Amide: Amides have an amine as their leaving group, which is a much worse leaving group due to the strong nucleophilicity and poor stabilizing ability. Thus, amides are the least reactive among these compounds.

Based on this reasoning, the correct order of reactivity towards nucleophilic substitution is: Acyl Chloride > Acid Anhydride > Ester > Amide.