C/5-l,2-dimethylcyclohexane

A molecule of c/5-l,2-dimethylcyclohexane can also exist in two conformations (see Fig. 9.12). In this case, the two are of equal stability (they are mirror images) since in each there is one equatorial and one axial —CH3 group. 

Next, let us make a model of c/5-l,2-dimethylcyclohexane and a model of its mirror image. We find they are not superimposable, and hence are enantiomers. 

Thus, just as with the cis- and rm/7j-l,2-cyclopentanediols (Sec. 9.13), we could assign configurations to the cis- and rra/75-l,2-dimcthylcyclohexanes by finding out which of the two is resolvable. The c/5-l,2-dimethylcyclohexane is not literally a meso compound, but it is a non-resolvable racemic modification, which for most practical purposes amounts to the same thing. 

Like the 1,4-dimethyl derivatives, 1,2-dimethylcyclohexane has a lower heat of combustion (see Table 3.2) and is more stable than c/5-l,2-dimethylcyclohexane. The cis stereoisomer has two chair conformations of equal energy, each containing one axial and one equatorial methyl group. 

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