Assertion (A): The two chair conformers of cis-1,2-dimethylcyclohexane have equal energy. Reason (R): Both chair conformers have two axial methyl groups.

Answer: C

In cis-1,2-dimethylcyclohexane one methyl is axial and one equatorial in each chair ((a,e)

\leftrightarrow

(e,a)), and each chair has the same set of interactions (one axial CH

_{3}

and one gauche CH

_{3}

/CH

_{3}

), so the energies are equal and the assertion is true. The reason is false, because neither chair is diaxial.