In cis-1,4-di-tert-butylcyclohexane, a chair necessarily has one tert-butyl group axial; assume this chair lies 26.0 kJ/mol above the all-equatorial reference, while the twist-boat with both tert-butyl groups pseudo-equatorial lies 23.0 kJ/mol above the same reference. Take R = 8.314 J/(K mol), 298 K, and neglect degeneracy. The percentage of molecules in the twist-boat form at equilibrium is closest to

Answer: A

The twist-boat is lower than the axial-tert-butyl chair by 3.0 kJ/mol. Ratio twist-boat/chair =

e^{3000/ (8.314 \times 298)} = e^{1.211} = 3.36

. Fraction twist-boat = 3.36/(1 + 3.36) = 77%. The chair fraction is 23%.