Use for cis-1,2-dimethylcyclohexane: CH3/H 1,3-diaxial interaction = 3.8 kJ/mol and gauche CH3/CH3 interaction = 3.8 kJ/mol. Select the correct statements.

AThe two chair conformers are of equal energy
BThe compound is a meso compound (it has a plane of symmetry in its planar-ring representation)
CA chair with both methyl groups equatorial is possible
DEach chair carries about 11.4 kJ/mol of strain from the interactions listed

Answer: A, B, D

In cis-1,2 one methyl is axial and one equatorial in each chair, so the two chairs are mirror-image conformers of equal energy. The cis isomer has a mirror plane when the ring is drawn flat, so it is meso. A diequatorial arrangement is possible only for trans-1,2. Each chair: axial methyl has two CH3/H interactions (7.6) plus one gauche CH3/CH3 (3.8) = 11.4 kJ/mol.

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Use for cis-1,2-dimethylcyclohexane: CH3/H 1,3-diaxial interaction = 3.8 kJ/mol and gauche CH3/CH3 interaction = 3.8 kJ/mol. Select the correct statements.

Answer: A, B, D

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