The most reactive of the carboxylic acid derivatives towards nucleophilic attack is

  • A. the amide
  • B. the ester
  • C. the carboxylate salt
  • D. the acyl chloride

Explanation

Chlorine is a good leaving group and withdraws electron density strongly, so the carbonyl carbon of an acyl chloride is highly electron deficient and it reacts violently even with cold water. Reactivity falls in the order acyl chloride, anhydride, ester, amide, since each successive group donates electron density more effectively. This is why acyl chlorides are the reagents of choice for making esters of unreactive alcohols and phenols.

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