See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Solution: Identifying the Compound Without Geometric Isomerism **Geometric isomerism requirement:** A compound shows geometric (cis-trans) isomerism when there is restricted rotation around a double bond with **two different groups on each carbon** of the double bond. **Analyzing each option:** **(A) Cyclopentane with two methyl groups:** - Ring structures allow free rotation and conformation changes - Does NOT show geometric isomerism (shows stereoisomerism instead) **(B) $Me$-$CH=CH$-$CH=CH$-$Et$ conjugated diene:** - First $C=C$: Me and H on one carbon; H and CH=CHEt on the other → **can show cis/trans** - Second $C=C$: H and CH=CHMe on one carbon; H and Et on the other → **can show cis/trans** - Shows geometric isomerism ✓ **(C) $MeCH=CH-CH=CHEt$ conjugated diene:** - First $C=C$: Me, H on one carbon; H, CH=CHEt on the other → **can show cis/trans** - Second $C=C$: H, CH=CHMe on one carbon; H, Et on the other → **can show cis/trans** - Shows geometric isomerism ✓ **(D) $Me$-$C(Et)=C(Me)$-$Et$:** - Both carbons of the double bond have **identical substituents**: each has Me and Et - Cannot distinguish between "cis" and "trans" arrangements - **Does NOT show geometric isomerism** ✗ **Answer: (D)** — The symmetry of substituents makes cis/trans forms identical, eliminating geometric isomerism.