One of the chair conformers of cis-1,3-dimethylcyclohexane is 5.4 kcal/mol less stable than the other. How much steric strain does a 1,3-diaxial interaction between two methyl groups introduce into the conformer

See explanation

Explanation:

the Cis structure, we can have two possibilities. The methyl groups can go both in axial positions or both in equatorial positions. We have to remember that cis it means "same orientation", so in the axial positions, both methyl groups go up. (Both have the same orientation). In the equatorial positions, both groups go down.

In the axial positions, we will have more steric hindrance because the groups are close to each other. Therefore, we will have more energy and the structure will be less stable. In the equatorial positions, we dont have any steric hindrances, so we will have less energy and more stability.

See figure 1

I hope it helps!