Numerical answers to the first exercise on modelling, using Arguslab

These are the results obtained by BWT, using the procedure set out in the instructions.  If you think BWT has any wrong answers, please tell him


Conformation E / Hartrees D/kJ mol-1 K E / Hartrees D/kJ mol-1 K
chair 0.01028931 -32.9699642394
36.99 3730892 17.12 1101
twist boat 0.02437778 -32.9634430443


Conformation of cyclohexane,
attachment point of methyl
E / Hartrees D/kJ mol-1 E / Hartrees D/kJ mol-1 D/kJ mol-1
0.01240431 0 -38.466028002 0 0
0.01540569 7.88 -38.464235271 4.707 7.44
twist boat,
to 'C2 axis' through bonds
0.02691854 38.11 -38.459404049 17.39 26.68
twist boat,
on C with 'C2 axis' through it
0.02759455 39.88 -38.459323632 17.60 24.61
twist boat,
to 'C2 axis' through bonds
0.02951179 44.92 -38.457904045 21.33 30.02

The differences are all relative to the 'chair, equatorial' conformer.  Energy differences by the MM2 force field method are quoted from J.M. Goodman  'Chemical Applications of Molecular Modelling'.  Note that the energy of two conformers are swapped over according to this method.  The energy differences by the UFF method are about twice those by the PM3 method, corresponding to squaring the equilibrium constant (if there were any way of measuring one of these sizes for this molecule)!

Pictures of the three twist-boat conformers of methylcyclohexane

These are unoptimised mock-ups quickly built from twist-boat cyclohexane, using the Molden Z-matrix editor, and converted from .xyz to a useful view and exported as a .gif file by Rasmol.  They may help you to be sure you have been looking at the right conformers.
twist boat,
methyl parallel 
to 'C2 axis' through bonds
twist boat,
methyl on C with 'C2 axis' through it
twist boat,
methyl perpendicular
to 'C2 axis' through bonds