Question

Identify the optically active cyclohexane from the given options.

• A. trans - $1$ , $3$-dimethyl cyclohexane
• B. cis- $1$ , $3$-dimethyl cyclohexane
• C. cis- $1$ , $4$-dimethyl cyclohexane
• D. frans- $1$ , $4$-dimethyl cyclohexane

Answer 1

Answer: (A)

cis- and trans - $1,4$-dimethylcyclohexane contain an internal symmetry plane, only two stereoisomers appear. Therefore, they are both meso compounds (optically inactive)

In contrast to $1,4$- dimethylcyclohexane, only cis-$1,3$- dimethylcyclohexane contains an internal symmetry plane, while trans-$1$, $3$ dimethylcyclohexane does not. Thus, cis-1, 3- dimethylcyclohexane is a meso compound, and trans-$1,3$-dimethylcyclohexane shows optical activity