Organic Chemistry MCAT Practice Exam

In a Newman projection, which configuration represents the lowest energy state?

1. Gauche

2. Syn

3. Anti

4. Eclipsed

The correct answer is: Anti

In a Newman projection, the lowest energy state corresponds to the configuration where the substituents on adjacent carbon atoms are as far apart as possible, minimizing steric repulsions. The anti configuration is characterized by the two largest substituents being positioned directly opposite each other, maximizing the distance between them and minimizing repulsive interactions. In contrast, other configurations such as gauche and syn positions bring substituents closer together, leading to increased steric strain and therefore higher energy states. The eclipsed configuration is particularly high in energy because the substituents are aligned with each other, resulting in significant torsional strain. Consequently, the anti configuration is the most stable and lowest energy arrangement in a Newman projection.