Organic Chemistry MCAT Practice Exam

Which reaction involves the formation of a tetrahedral intermediate?

1. Saponification

2. Esterification

3. Hydrolysis

4. Nitration

The correct answer is: Esterification

The formation of a tetrahedral intermediate is a characteristic feature of nucleophilic acyl substitution reactions, such as those involving esters and carboxylic acids. In esterification, a nucleophile (like an alcohol) attacks the electrophilic carbon of the carbonyl group in a carboxylic acid or an ester. This results in the formation of a tetrahedral intermediate where the carbonyl bond is broken and the oxygen atom from the alcohol forms a new bond with the carbon atom. This tetrahedral intermediate is a transient species that then rearranges, allowing the original carbonyl carbon to regain its double bond while expelling a leaving group, typically water or an alcohol. This mechanism is essential for understanding how esters are formed from carboxylic acids and alcohols. In contrast, while saponification and hydrolysis also involve nucleophilic attack on carbonyls, they do not emphasize the tetrahedral intermediate formation in the same clear way that esterification does. Nitration, on the other hand, involves electrophilic aromatic substitution and does not form a tetrahedral intermediate at all, focusing instead on the formation of a sigma-complex in aromatic systems. Thus, esterification is the most suitable answer for this question, as