Table 3-6 shows that the axial-equatorial energy difference for methyl, ethyl, and isopropyl groups increases gradually: 7.6, 7.9, and 8.8 kJ mol (1.8, 1.9, and 2.1 kcal mol). The tertbutyl group jumps to an energy difference of 23 kJ mol (5.4 kcal mol), over twice the value for the isopropyl group. Draw pictures of the axial conformations of isopropylcyclohexane and tert-butylcyclohexane, and explain why the tert-butyl substituent experiences such a large increase in axial energy over the isopropyl group.

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Energy Differences Between the Axial and Equatorial Conformations of Monosubstituted Cyclohexanes AG (axia-equatorial) (kJ/mol) (kcal/mol) 0.8 0.8 2.1 2.5 0.2 0.2 0.5 0.6 1.0 X Br -OH -COOH -CH -CH2CH axial equatorial 7.6 1.9 -CHCH 8.8 2.1 23 ーC(CH3)3