Draw the two chair conformations of cis-1-chloro-2-methylcyclohexane. Which is more stable, and by how much?

Four conformations are possible for cyclohexane: a chair, twist boat, boat, and half chair. Among all the four conformations chair form of cyclohexane is considered a very stable one. Chair conformation of cyclohexane is as follows;

Chair form of cyclohexane

We can say if the relation is up-up, then cis; if down–a down relationship, then trans.

If the up-down or down-up relation between the bond, then trans.

The two chair conformation of cis-1-chloro-2-methylcyclohexane are shown as follow;

If we compare both of them, it is seen that the left-hand side confirmation$\text{-Cl}$ group is in the axial position. Hence this group shows 1, 3 diaxial interaction, decreasing the stability of cis-1-chloro-2-methylcyclohexane.

Flipping the ring shows that on the right-hand side structure, the chlorine group occupies the equatorial, and the methyl group occupies the axial position. Hence this group shows 1, 3 diaxial interaction, so it decreases the stability of cis-1-chloro-2-methylcyclohexane.

But if we compare the value of diaxial strain, the value of strain for chlorine is 1.0 KJ/mol and for methyl group is 3.8 kJ/mol. Hence the structure on the left-hand side is more stable than on the right-hand side.