Cyclohexane exists its two chair conformations in rapid equilrium at room temperature.
Each carbon atom on a cyclohexane ring has one axial and one equatorial hydrogen. Ring-flipping converts axial II's to equatorial H's and vice-versa.

In substituted cyclohexane, groups larger than hydrogen are more stable in the equatorial position.
The cis isomer has two groups on the same side of the ring, either both up or both down.
The trans isomer has two groups on opposite side of the ring one up and one down.
Which of the following is most stable conformer of 1,2-dichlorocyclohexane?

Options

A.
B.
C.
D. All have equal stability

Answer

B

Explanation

No repulsion at equatorial position.