Organic Chemistry MCAT Practice Exam

What is the most stable conformation of a cyclohexane ring?

1. Boat conformation

2. Chair conformation

3. Twist conformation

4. Planar conformation

The correct answer is: Chair conformation

The most stable conformation of a cyclohexane ring is the chair conformation. In this arrangement, the bond angles are approximately 109.5 degrees, which is ideal for sp³ hybridized carbon atoms. This conformation allows for minimized steric strain and torsional strain within the ring structure. In the chair conformation, all carbon-carbon bonds are staggered, reducing torsional strain. Additionally, the axial and equatorial positions allow for optimal placement of substituents. When groups are in the equatorial position, they experience less steric hindrance compared to the axial position, contributing further to the overall stability of the cyclohexane. In contrast, the boat conformation suffers from both steric and torsional strain due to the proximity of hydrogens that are aligned in an eclipsed fashion, making it less favorable. The twist conformation offers a slight improvement over the boat but does not reach the stability of the chair conformation. The planar conformation is highly unstable for cyclohexane, as it does not allow for the proper bond angles and leads to considerable angle strain. Overall, the chair conformation is the lowest energy state for cyclohexane, making it the most stable conformation of the