How many isomers (constitutional and stereoisomers) exist for dimethylcyclohexane?

Question

Quizplus · Accepted Answer

Dimethylcyclohexane can exist in several isomeric forms due to the different positions the two methyl groups can occupy on the cyclohexane ring, as well as the chair conformations of cyclohexane which can lead to cis-trans isomerism. Specifically, there are three positional isomers: 1,1-dimethylcyclohexane, 1,2-dimethylcyclohexane, and 1,3-dimethylcyclohexane. Each of these can exist in different stereoisomeric forms due to the cyclohexane chair conformations, except for 1,1-dimethylcyclohexane which does not have cis-trans isomerism. 1,2-dimethylcyclohexane has three stereoisomers (cis, trans, and another cis due to the chair flip), and 1,3-dimethylcyclohexane has four (two cis and two trans, again due to chair flips). Adding these up gives a total of 9 isomers.

How Many Isomers (Constitutional and Stereoisomers) Exist for Dimethylcyclohexane