See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Determining Meso Form Existence **Step 1: Understand meso compound requirements** A meso compound must have: - Two or more chiral centers - An internal plane of symmetry - Equal and opposite stereochemistry at corresponding stereocenters (achiral despite having chiral centers) **Step 2: Analyze each option** **(A) 1,2-dichlorobutane:** $CH_3-CHCl-CHCl-CH_3$ - Two chiral centers at C2 and C3 - No plane of symmetry (the end groups $CH_3$ and $CH_3$ are identical, but overall molecule lacks internal symmetry) - Cannot exist as meso form ✗ **(B) 2,3-dichloropentane:** $CH_3-CHCl-CHCl-CH_2-CH_3$ - Two chiral centers at C2 and C3 - End groups are different ($CH_3$ vs $CH_2CH_3$) - No plane of symmetry possible ✗ **(C) 2,3-dichlorobutane:** $CH_3-CHCl-CHCl-CH_3$ - Two chiral centers at C2 and C3 - Vertical plane of symmetry through the C2-C3 bond - With (R,S) and (S,R) configurations → meso form exists - Internally symmetric ✓ **(D) 1,2-dichloropentane:** $CHCl_2-CHCl-CH_2-CH_2-CH_3$ - Two chiral centers but asymmetric end groups - No internal plane of symmetry ✗ **Answer: (C) 2,3-dichlorobutane** is the only compound with identical end groups ($CH_3$ on both sides), allowing an internal plane of symmetry and enabling a meso form to exist.