Question: Draw both conformations for 1-ethyl-1-methylcyclohexane and decide which conformation (if any) is more stable.

The stereoisomers that can be easily interconverted into one another by rotating about the carbon-carbon sigma bonds are called conformational isomers.

The interconversion of the conformational isomers can also take place at room temperature.

The following structures show the conformational isomers of 1-ethyl-1 methylcyclohexane:

Isomer of 1-ethyl-1-methylcyclohexane

In the above structure, a methyl group ($-C{H}_3$) is present at the equatorial position, and the ethyl group ( $-C{H}_{2}C{H}_3$) is present at the axial position. The above structure is less stable because a bulky ethyl group is present at the axial position.

If present at the axial position, the ethyl group will face 1,3 di axial repulsions, making the structure less stable.

Isomer of 1-ethyl-1-methylcyclohexane

In the above structure, the bulky group, i.e., the ethyl group, is present equatorial. It will face less repulsions from the neighboring groups. As a result, the above structure (II) will be more stable.