In cis-1-tert-butyl-4-methylcyclohexane the A-values are tert-butyl 20.0 and methyl 7.3 kJ/mol (strain of the axial position relative to equatorial; assume additivity). The more stable chair is more stable than the other chair by

A $27.3 kJ mo l^{- 1}$
B $12.7 kJ mo l^{- 1}$
C $7.3 kJ mo l^{- 1}$
D $20.0 kJ mo l^{- 1}$

Answer: B

In cis-1,4 one group is axial and one equatorial in either chair. One chair has axial methyl (strain 7.3) and the other axial tert-butyl (strain 20.0). The difference = 20.0 - 7.3 = 12.7 kJ/mol, with tert-butyl equatorial and methyl axial in the more stable chair.

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