Which of the following molecules is a meso compound?

• A. $2,3-\mathrm{dimethylpentane}$
• B. $1,2-\mathrm{dichloropropane}$
• C. $2,3-\mathrm{dibromobutane}$
• D. $2,3-\mathrm{butanediol}$

Answer: (C)

Verified step by step guidance

1. Identify the structure of each compound mentioned: 2,3-dimethylpentane, 1,2-dichloropropane, 2,3-dibromobutane, and 2,3-butanediol. Draw their skeletal formulas to visualize the stereocenters and substituents clearly.
2. Determine the number and position of stereocenters (chiral centers) in each molecule. A stereocenter is typically a carbon atom bonded to four different groups.
3. Check for internal planes of symmetry in each molecule. A meso compound must have stereocenters but also possess an internal plane of symmetry that makes it achiral overall.
4. Analyze the stereochemistry of the stereocenters: if the molecule has stereocenters but is superimposable on its mirror image due to symmetry, it is meso. For example, in 2,3-dibromobutane, examine if the two stereocenters have opposite configurations (R and S) and if the molecule is symmetric.
5. Conclude which molecule is meso by confirming it has stereocenters and an internal plane of symmetry, making it achiral despite having chiral centers.