Organic Chemistry MCAT Practice Exam

Which of the following is a property of more substituted carbanions?

1. More stable

2. Less stable

3. Neutral

4. Non-existent

The correct answer is: Less stable

The correct answer to the question regarding the stability of more substituted carbanions is that they are more stable. In organic chemistry, the stability of carbanions largely depends on the substituents attached to the negatively charged carbon atom. In a more substituted carbanion, the presence of additional alkyl groups can stabilize the negative charge through several mechanisms. Alkyl groups can donate electron density through inductive effects, which helps to disperse the negative charge across the molecule. Additionally, hyperconjugation—where adjacent C-H or C-C bonds interact with the empty p orbital of the carbanion—further stabilizes the carbanionic species. Generally, as the number of substituents increases, the stability of the carbanion also increases, making the statement about more substituted carbanions being more stable accurate. This is contrary to the answer provided, which suggests that more substituted carbanions are less stable, a concept that does not align with the established understanding of carbanion stability in organic chemistry.