Question

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

Short answer

a.

Formation of carboxylic acid derivative

b.

No reaction takes place

c.

Formation of a mixture of carboxyli

Step-by-step solution

Step-by-Step Solution Step 1: Acyl substitution reaction

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.

Formation of the products

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