Cyclohexane Conformations

Methyl and DimethylCyclohexanes

The ring flipping conformational change in cyclohexane interconverts equatorial and axial positions on the ring, thus placing equatorial and axial substituents in equilibrium with each other.

In general, the position of the equilibrium strongly favors the equatorial conformers.

Axial groups are in a gauche arrangement with the ring carbons numbers 3- and 5-
For a methyl group each one of these interactions contributes about 0.9 kcal/mol of strain energy
Other groups may have gauche energies greater or smaller than this
- The energy of an axial tert-butyl (1,1-dimethylethyl) group is so great that the equilibria for rings containing this group lie entirely to the side of the equatorial conformer

In the Java windows below, orient the molecules so you can look along the bonds between the carbon bearing the methyl group and one of the adjacent carbons.

You should see one gauche interaction when you look down the left-hand bond and another when you look down the right-hand bond

Equatorial

Axial

If you use the button to make the model spacefilling, you can see the Hs of the methyl mashed up against the Hs on the carbons 3- and 5-.

Here is (1,1-dimethylethyl)cyclohexane. See how distored the ring is, flattened at one end to allow the big group to tilt away from the hydrogens of carbons 3- and 5-.

tert-ButylCyclohexane

Click through to the next page to begin looking at the dimethylcyclohexanes

This page last modified 11:49 AM on Saturday September 19th, 2009.
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