See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

**Analysis of Geometrical Isomerism in Dichloropentenes** Geometrical (cis-trans) isomerism requires: 1. A carbon-carbon double bond 2. Two different groups attached to each carbon of the double bond **Examining each option:** **(A) 1,2-dichloro-1-pentene:** $CHCl=CHCHCl_2$ - Double bond: $C=C$ with $Cl$ on C1 and $H$ on C2 - Different groups on each carbon → **cis-trans isomerism exists** ✓ **(B) 1,3-dichloro-2-pentene:** $CH_2Cl-CH=C(Cl)CH_2CH_3$ - Double bond carbons: one has $Cl$ and $CH_2CH_3$; other has $Cl$ and $CH_2Cl$ - Different substituents on each carbon → **cis-trans isomerism exists** ✓ **(C) 1,1-dichloro-1-pentene:** $CCl_2=CHCH_2CH_2CH_3$ - Double bond carbons: C1 has **two identical $Cl$ groups**, C2 has $H$ and alkyl - One carbon has identical substituents → **NO geometric isomerism** ✗ **(D) 1,4-dichloro-2-pentene:** $CH_2Cl-CH=CH-CH_2Cl$ - Double bond: each carbon has one $H$ and one alkyl group - Both carbons have identical pattern → **cis-trans isomerism exists** ✓ **Answer: (C)** — 1,1-dichloro-1-pentene does not show geometrical isomerism because the sp² carbon bearing the double bond has two identical chlorine atoms, violating the requirement for two different groups on the same carbon.