Question

The relative rate of nucleophilic acyl substitution for a given acid derivative (RCOX) depends on :

• A. only the resonance effect of X.
• B. both the resonance effect and inductive effect of X.
• C. only the inductive effect of X.
• D. neither the resonance effect nor the inductive effect.

Answer 1

The correct option is B both the resonance effect and inductive effect of X.

A nucleophile is an electron rich species that will react with an electron poor species (Nu in scheme). An acyl group is $R-C=O$ (where R can be alkyl or aryl). Note that the acyl group is in both the starting material and the product.
In substitution, the leaving group (LG) is replaced by the nucleophile (Nu). There are two fundamental events in a nucleophilic acyl substitution reaction:
Formation of the new s-bond to the nucleophile, Nu.
Breaking of the s-bond to the leaving group, LG.
In acid derivative R- COX, greater - I effect and smaller +R effect of 'X' increases reactivity in nucleophilic substitution reaction.