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 and inductive effect of X
C.Only the inductive effect of X
D.Neither the resonance effect nor the inductive effect

Answer 1

To answer this question, you must recall the mechanism of nucleophilic acyl substitution. Nucleophilic acyl substitution is a class of substitution reactions that involves nucleophiles and acyl compounds. The nucleophile in these reactions substitutes the leaving group present on the acyl group, like an alcohol displacing halide from an acid halide.

Complete step by step answer:
The reactivity of the acyl derivatives depend majorly on two factors, namely the ease of departure of the leaving group and the resonance effects of the leaving group, that is, X.
The substitution reaction involves the breaking of bond with the leaving group and formation of bond with the nucleophile. The resonance of the leaving group with the acyl oxygen results in the formation of a double bond between the leaving group and the carbon atom thus, making it difficult for the bond to break. We can say more the resonance effect less is the rate of nucleophilic acyl substitution.
Once the nucleophile attacks, a tetrahedral intermediate is formed and the resonance effect is lost. Now the stronger the electron withdrawing inductive effect of the leaving group, easier would be the cleavage of the bond and thus faster would be the rate. Due to this reason, acid chlorides are most reactive acid derivatives.
Thus, we can say that the rate of nucleophilic acyl substitution depends both on the resonance and inductive effect of the leaving group.

Thus, the correct answer is B.

Note:
Acyl derivatives are reactive compounds due to the presence of an electrophilic carbon atom and react with a vast variety of nucleophiles. Thus, nucleophilic acyl substitution is a very common reaction in the synthesis of a variety of different compounds.