Which one of the following compounds can exist as cis-trans isomers?

Question

Which one of the following compounds can exist as cis-trans isomers?

1. A. Pent-1-ene
2. B. 2-Methylhex-2-ene
3. C. 1,1-Dimethylcyclopropane
4. D. 1,2-Dimethylcyclohexane (Correct answer)

Correct Answer

Option D — 1,2-Dimethylcyclohexane

Detailed Solution & Explanation

The correct answer is 1,2-Dimethylcyclohexane.

Key Points

• Geometrical (cis-trans) isomerism needs restricted rotation and two different groups on each of the two centres.
• 1,2-Dimethylcyclohexane has two methyls on adjacent ring carbons that can be on the same side (cis) or opposite sides (trans).
• Pent-1-ene and 2-methylhex-2-ene have a terminal/di-substituted carbon with two identical H (no cis-trans); 1,1-dimethylcyclopropane has both methyls on one carbon (no cis-trans).