Based on a knowledge of the stability of the conformers of cyclohexane, which of the following statements is true about the isomers of 1,2-dimethylcyclohexane?
A) The cis-isomer will have two equatorial methyl substituents in its most stable conformation.
B) The trans-isomer will have two axial methyl substituents in its most stable conformation.
C) The trans-isomer will have two equatorial methyl substituents in its most stable conformation.
D) The cis-and trans-isomers are equally stable.

Question

Quizplus · Accepted Answer

The most stable conformation of cyclohexane is the chair conformation, where all substituents are either axial or equatorial. In 1,2-dimethylcyclohexane, both the cis and trans isomers are possible, and in both cases, one methyl group will be axial and the other will be equatorial in the most stable conformation. However, due to steric hindrance between the two methyl groups, the trans-isomer will have a lower energy conformation if both methyl groups are equatorial. Therefore, the trans-isomer will have two equatorial methyl substituents in its most stable conformation (Choice C).

Based on a Knowledge of the Stability of the Conformers