See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Optical Isomerism Analysis **Optical isomerism** occurs when a compound has a chiral center (asymmetric carbon with four different groups attached). **Checking each option:** **(1) 1,2-Propadiene:** $CH_2=C=CH_2$ - Has two double bonds (cumulative) - The central carbon has two identical $CH_2$ groups - **No chiral center** → No optical isomerism **(2) 2,3-Pentadiene:** $CH_3CH=C=CHCH_3$ - Cumulative double bonds with different groups on the terminal carbons - The allenes structure creates an axial chiral center - **Shows optical isomerism** ✓ **(3) sec-Butyl alcohol:** $CH_3CH(OH)CH_2CH_3$ - The second carbon is bonded to: $H$, $OH$, $CH_3$, $C_2H_5$ (all different) - **Has a chiral center** → Shows optical isomerism ✓ **(4) 2,3-Butanediol:** $CH_3CH(OH)CH(OH)CH_3$ - Both carbons 2 and 3 are chiral centers - **Shows optical isomerism** ✓ **Answer: (1) 1,2-Propadiene** cannot show optical isomerism because it lacks a chiral center—the central carbon is bonded to two identical methylene groups.