See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Geometrical Isomerism Analysis **Understanding Geometrical Isomerism Requirements:** Geometrical isomerism occurs when: 1. A double bond is present (restricted rotation) 2. Two different groups attach to each carbon of the double bond **Analyzing Each Option:** **(A) Cyclopentene:** - Has one $C=C$ double bond - Both carbons of the double bond each have one H atom - Structure: $\ce{CH=CH}$ with identical H groups - **No geometrical isomerism** (identical groups on each carbon) **(B) Dimethylcyclohexene:** - Double bond present in the ring - Both methyl groups ($CH_3$) attach to the same carbon atom of the double bond - **No geometrical isomerism** (both substituents on one carbon) **(C) Benzene:** - Aromatic ring with delocalized electrons - No fixed double bonds with restricted rotation - **No geometrical isomerism** (aromatic stability prevents geometric variation) **(D) Cyclooctene (8-membered ring with one double bond):** - Contains a $C=C$ double bond - In the ring geometry, each double bond carbon has different groups attached (H and different ring portions) - The ring is large enough that substituents can be forced into **cis and trans positions** relative to the double bond - **Geometrical isomerism IS possible** (cis and trans isomers exist) **Answer: (D)** — The 8-membered ring is large enough to allow restricted rotation around the double bond, enabling cis-trans isomerism.