NEET 2025 · ChemistryPrevious Year Question
Which one of the following compounds can exist as cis-trans isomers?
- A.1,1-Dimethylcyclopropane
- B.1,2-Dimethylcyclohexane✓
- C.Pent-1-ene
- D.2-Methylhex-2-ene
Correct Answer
(B) 1,2-Dimethylcyclohexane
Solution & Explanation
\textbf{Answer:} (b) \textbf{Solution:} Cis-trans (geometrical) isomerism requires two different groups on each of two carbons whose relative spatial arrangement is fixed by a ring or a C=C double bond. In 1,2-dimethylcyclohexane the two methyls are on adjacent ring carbons and can lie on the same face (cis) or opposite faces (trans). 1,1-Dimethylcyclopropane has both methyls on one carbon (no cis/trans); pent-1-ene has a terminal $\ce{=CH2}$ (two identical H); and in 2-methylhex-2-ene one doubly-bonded carbon bears two identical methyl groups, so neither of these shows cis-trans isomerism.
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