See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Geometric Isomerism in Alkenes **Geometric isomerism (cis-trans isomerism) requires:** 1. A C=C double bond 2. Two different groups attached to each carbon of the double bond **Analyzing each option:** **(A) 1-Phenyl-2-butene:** $C_6H_5-CH=CH-CH_2-CH_3$ - Double bond carbons: one has $C_6H_5$ and $H$; the other has $H$ and $CH_2CH_3$ - All four groups are different ✓ - Exhibits **cis and trans isomers** ✓ **(B) 3-Phenyl-1-butene:** $CH_2=CH-CH(C_6H_5)-CH_3$ - One double bond carbon has two $H$ atoms - Cannot show geometric isomerism (identical groups on one carbon) ✗ **(C) 2-Phenyl-1-butene:** $CH_2=C(C_6H_5)-CH_2-CH_3$ - One double bond carbon has two $H$ atoms - Cannot show geometric isomerism ✗ **(D) 1,1-Diphenyl-1-propene:** $(C_6H_5)_2C=CH-CH_3$ - One double bond carbon has two identical phenyl groups - Cannot show geometric isomerism ✗ **Answer: (A)** — Only 1-phenyl-2-butene has all four different substituents on its double bond carbons, allowing cis-trans isomers.