See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Analysis of Optical Isomerism Optical isomerism requires a **chiral center** (asymmetric carbon with four different groups attached). ## Option (A): $CH_3\text{-}CH=C=CH\text{-}CH_3$ - Contains a **cumulated double bond** ($C=C=C$) - The central carbon in allene has sp hybridization with only 2 substituents - **No chiral center** → No optical isomerism ✗ ## Option (B): Cyclopentene with exocyclic double bond - The $=C$ carbon is part of a double bond with two substituents ($CH_3$ and $Cl$) - Double bond carbons cannot be chiral centers (only 3 different groups possible) - **No optical isomerism** ✗ ## Option (C): Cyclohexane with exocyclic double bond and Cl, H on ring - The double bond carbon ($=C(CH_3)(Cl)$) has only 3 different groups - The ring carbon bearing Cl and H is adjacent to the double bond but is saturated - Examining the cyclohexane ring: the stereogenic carbon is part of the ring and attached to $Cl$, $H$, and two different ring carbons - **This carbon IS chiral** → **Shows optical isomerism** ✓ ## Option (D): Substituted biphenyl - Both aromatic rings are planar and rigid - The single bond connecting them doesn't allow free rotation to create distinct enantiomers under normal conditions - **No optical isomerism** (atropisomerism is not typically considered here) ✗ **Answer: (C)** shows optical isomerism due to a chiral center on the cyclohexane ring carbon bearing Cl and H.