Question

When methyl group is in axial position in methyl cyclohexane, the molecule has:

• A. one Gauche interaction
• B. two Gauche interaction
• C. no Gauche interaction
• D. three Gauche interaction

Answer 1

The correct option is B two Gauche interaction

There is a gauche interaction between the axial methyl group and C-3. This is absent in the conformation where methyl is equatorial. This gauche interaction is an example of [van der waals strain] is what makes the axial conformer higher in energy.

There is actually a second gauche interaction if you look along C-1 to C-6 . This gauche interaction is with C-5.

The methyl group interacting with the other ‘axial’ hydrogens, at C-3 and C-5. These are called “diaxial interactions” since they are steric interactions between axial substituents.