See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Geometrical Isomerism Analysis Geometrical isomerism requires: - A C=C double bond (restricted rotation) - **Different groups on at least one carbon atom** of the double bond Let me evaluate each structure: **Structure (1):** $(CH_3)_2C=CH_2$ - Left carbon: two identical $CH_3$ groups - Right carbon: two identical $H$ atoms - ❌ No geometric isomers possible (identical groups on both carbons) **Structure (2):** $CH_2=CHCH_3$ - Left carbon: two identical $H$ atoms - Right carbon: one $H$ and one $CH_3$ - ❌ No geometric isomers (left carbon has identical groups) **Structure (3):** $CH_3CH=CHCH_3$ (but-2-ene) - Left carbon: one $CH_3$ and one $H$ ✓ - Right carbon: one $CH_3$ and one $H$ ✓ - ✅ **Different groups on BOTH carbons** → **cis-trans isomerism possible** - *cis*: both $CH_3$ on same side - *trans*: $CH_3$ groups on opposite sides **Structure (4):** $CH_3CH=C(CH_3)_2$ - Left carbon: one $CH_3$ and one $H$ ✓ - Right carbon: two identical $CH_3$ groups - ❌ No geometric isomers (right carbon has identical groups) **Answer: (3)** - Only but-2-ene satisfies the requirement of having different substituents on both sp² carbons of the double bond, enabling cis-trans geometric isomerism.