See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Finding the Meso Isomer A **meso compound** has chiral centers but is achiral overall due to an internal plane of symmetry. ## Analysis of Each Option: **(1) 2,3-Dichloropentane** - Structure: $CH_3\text{-}CHCl\text{-}CHCl\text{-}CH_2CH_3$ - Has 2 chiral centers (C2 and C3) - No internal plane of symmetry → produces optical isomers only, no meso form ✗ **(2) 2,3-Dichlorobutane** ✓ - Structure: $CH_3\text{-}CHCl\text{-}CHCl\text{-}CH_3$ - Has 2 chiral centers (C2 and C3) - The two halves are **identical** ($CH_3$ groups at both ends) - **Meso form exists**: When both $Cl$ atoms are on opposite sides (one wedge, one dash), an internal plane of symmetry passes through C2-C3 bond - This meso isomer is achiral despite having chiral centers ✓ **(3) 2-Chlorobutane** - Only 1 chiral center → cannot be meso (meso requires ≥2 chiral centers with symmetry) ✗ **(4) 2-Hydroxypropionic acid** - Only 1 chiral center → cannot be meso ✗ ## Answer: **(2) 2,3-Dichlorobutane** has a meso isomer because its two chiral centers are identical (both bonded to $CH_3$ groups), allowing for an internal plane of symmetry in the anti configuration.