What is the product of an acyl substitution reaction—a new carboxylic acid derivative, a mixture of two carboxylic acid derivatives, or no reaction—if the new group in the tetrahedral intermediate is the following?

a. a stronger base than the substituent that is attached to the acyl group

b. a weaker base than the substituent that is attached to the acyl group

c. similar in basicity to the substituent that is attached to the acyl group

When a nucleophile attacks an electrophilic carbon, the weakest bond in the molecule breaks. The weakest bond in a ${\mathbf{S}}_N\mathbf{2}$reaction is the bond which is attached to the leaving group, so this is the bond that breaks. The weaker the base, the better it is as a leaving group. In contrast, the weakest bond in a nucleophilic acyl substitution reaction is the pi bond, so this bond breaks first and the leaving group is eliminated.

a)

The mechanism for the nucleophilic addition-elimination reaction involves the formation of a tetrahedral intermediate.

In the intermediate, the weaker base of the two bases is eliminated. Due to the addition of a strong base, the group attached to the acyl group in the reactant is eliminated. This results in the formation of carboxylic acid derivatives. For example:

Formation of carboxylic acid derivative

b)

The mechanism for the nucleophilic addition-elimination reaction involves the formation of a tetrahedral intermediate. In the intermediate, the weaker of the two bases is eliminated. Because a weaker base is added, a newly added group after it has lost a proton is eliminated. This results in the re-formation of the reactants. Hence, no reaction takes place.

No reaction takes place

c)

The mechanism for the nucleophilic addition-elimination reaction involves the formation of a tetrahedral intermediate. In the intermediate, the weaker of the two bases is eliminated. Because a similar basicity group is added, it results in the formation of a mixture of carboxylic acid derivatives.

Formation of a mixture of carboxylic acid derivatives