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

Answer: (A)

Acylchloride $>$ Acid anhydride $>$ Ester $>$ Amide
The ease of nucleophilic substitution depends upon the nature of leaving group. When the leaving tendency of a group in a compound is high, then the compound is more reactive towards nucleophilic substitution.
The nucleophilic acyl substitution is completed in $2$ step. The reactivity of the compound may be explained by the basicity of leaving the group. A weaker base is a better leaving group.
The order of basicity is as;
$C{l}^{-}<RCO{O}^{-}<R{O}^{-}<N{H}_2^{-}$
Hence order of leaving tendency is $C{l}^{-}>RCO{O}^{-}>R{O}^{-}>N{H}_2^{-}$and therefore the order of reactivity of acyl compound is as;
Acylchloride $>$ Acid $\backslash$ Anhydride $>$ Ester $>$ Amide