[nupatel87]

So I am doing a practice exam for my organic chemistry exam and I came upon a question I am having a bit of trouble with. I have to make the two chair conformations for a trans-trisubstituted cyclohexane and then calculate the strain energies to determine which conformation is more stable. There is a Cl on Carbon 1 and a CH(CH3)2 on Carbon 4 that both face downward, and CH3 on Carbon 2 toward the upward face.

I understand how to draw the chair conformations, but how does one calculate the strain energies? I know the 1-3 diaxial strain energies and gauche strain and how they interact on mono/disubstituted cyclohexane chair conformations, but what is different on a trisubstitution?.

The answer keys state that the strains are 10.5 kj/mol for the normal chair and 9.6kj/mol for the ring flip. I calculated 7.6kj/mol and 7.2kj/mol for the ring flip.

Any idea on how to find out the energies? Thanks in advance.