Question

For ONE methyl group the a-e energy difference is 1.7 kcal/mol. What would be the aa-ee energy difference

     expected if there are TWO methyl groups on the ring?

Answer 1

Only 1,3-diaxial syn interactions will have an energy value on cyclohexane chair conformation, no such interactions for equatorial does not give any energy value. Hence

aa for two methyl groups give 2 x 1.7 kcal/mol = 3.4 kcal/mol at 1,2 disubstitution

aa for two methyl groups give 2 x 1.7 kcal/mol = 3.4 kcal/mol at 1,3 disubstitution

aa for two methyl groups give 2 x 1.7 kcal/mol = 3.4 kcal/mol at 1,4 disubstitution

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                                                           Total = 10.2 kcal/mol energy difference

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