Organic Chemistry MCAT Practice Exam

In imine formation, what type of amine acts as the nucleophile?

1. Primary amine

2. Secondary amine

3. Tertiary amine

4. All types of amines

The correct answer is: Primary amine

In the process of imine formation, a primary amine serves as the nucleophile. This reaction involves the interaction between a carbonyl compound, such as an aldehyde or ketone, and a primary amine. The nucleophilic nitrogen in the primary amine has a lone pair of electrons that can readily attack the electrophilic carbon of the carbonyl group, resulting in the formation of an intermediate that eventually leads to an imine. Primary amines contain one alkyl or aryl group attached to the nitrogen, which allows for a sufficient electronic environment for nucleophilicity. In contrast, secondary amines, which have two organic substituents on the nitrogen, can also act as nucleophiles but have steric hindrance that may make the reaction less favorable compared to primary amines. Tertiary amines, having three substituents on the nitrogen, lack a hydrogen that can participate in the formation of an imine and typically do not react with carbonyl compounds to form imines. Thus, the role of the primary amine as the nucleophile in imine formation is attributed to its optimal balance of reactivity and sterics, making it the most suitable choice in this process.