Which of the following is a meso compound?

• A. $2,3$-dibromopentane (with stereochemistry: $(2^R,3^R)-2,3$-dibromopentane)
• B. $3,4$-dihydroxyhexane (with stereochemistry: $(2^R,3^S)-3,4$-dihydroxyhexane)
• C. $2,3$-butanediol (with stereochemistry: $(2^R,3^R)-2,3$-butanediol)
• D. Tartaric acid (with stereochemistry: $(2^R,3^S)$-tartaric acid)

Answer: (D)

Verified step by step guidance

1. Recall that a meso compound is an achiral molecule that contains multiple stereocenters and an internal plane of symmetry, making it optically inactive despite having chiral centers.
2. Identify the stereocenters in each compound and analyze their configurations. For example, look at the (2R,3R) or (2R,3S) designations to understand the spatial arrangement of substituents.
3. Check for the presence of an internal plane of symmetry in the molecule. This plane divides the molecule into two mirror-image halves, which is a key feature of meso compounds.
4. Evaluate each compound: for instance, tartaric acid with (2R,3S) stereochemistry is known to have such a plane of symmetry, making it a classic example of a meso compound.
5. Conclude that the compound with stereocenters arranged so that the molecule is superimposable on its mirror image (achiral) and has an internal plane of symmetry is the meso compound.