Select the correct statements about trans-1,4-dimethylcyclohexane.

AIts more stable chair has both methyl groups equatorial
BIts two chair conformers have equal energy
CIts diaxial chair has four CH3/H 1,3-diaxial interactions
DIt is optically active because it has two stereocentres

Answer: A, C

In trans-1,4 the groups are both equatorial or both axial, so the diequatorial chair is much more stable and the two chairs are not equal. Each axial methyl has two 1,3-diaxial CH3/H interactions, giving four in the diaxial chair. The molecule has a mirror plane (and centre of symmetry), so it is achiral and optically inactive.

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