An optically active compound A with molecular formula C 8 H 14 undergoes catalytic hydrogenation to give an optically inactive product. Which of the following can be the structure of A?

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Ans. (D) A & B.

Sol. The product of hydrogenation must be an achiral dimethylcyclohexane while A itself must be chiral.

(A) cis-3,5-Dimethylcyclohex-1-ene is chiral (no plane of symmetry); hydrogenation gives cis-1,3-dimethylcyclohexane, which is meso and achiral.

(B) 1,4-Dimethylcyclohex-1-ene is chiral (C₄ is a stereocentre); hydrogenation gives 1,4-dimethylcyclohexane, which is achiral.

(C) cis-4,5-Dimethylcyclohex-1-ene itself has a plane of symmetry, so it is optically inactive and cannot be A.

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