Concept:A meso compound is an achiral molecule that contains multiple chiral centers but possesses an internal plane of symmetry.
Solution:- To have a plane of symmetry, the two halves of the molecule must be identical.
- 2,3-dichlorobutane: \( \text{CH}_3\text{--CH}(\text{Cl})\text{--CH}(\text{Cl})\text{--CH}_3 \). It has two chiral centers (C2 and C3) with identical substituent sets.
- In the (2R, 3S) or (2S, 3R) configuration, the molecule can be rotated to show a plane of symmetry splitting the C2-C3 bond.
- Thus, it exists as a meso isomer.
Why other options are incorrect:2-chlorobutane and 1,2-dichlorobutane lack symmetric halves. 2,3-dichloropentane has different ends (an ethyl group vs a methyl group), preventing an internal plane of symmetry.
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