Mesotartaric

Mesotartaric, or meso-tartaric acid, is the achiral stereoisomer of tartaric acid. Its chemical formula is C4H6O6, and it is one of three stereoisomers of tartaric acid: the pair of enantiomers D-tartaric acid and L-tartaric acid, and the meso form.

The meso form has two stereocenters at carbon atoms 2 and 3 with opposite configurations, typically described as (2R,3S) or (2S,3R). Because of an internal plane of symmetry, mesotartaric acid is optically inactive, meaning it does not rotate plane-polarized light.

In solution and in salts, mesotartaric acid behaves similarly to other tartaric acids. It is a diprotic acid, possessing two carboxyl groups, and it can form tartrate salts. However, unlike the enantiomeric pair, it does not contribute to optical activity and is often encountered as a distinct diastereomer in chemical studies.

Occurrence and preparation vary: mesotartaric acid can be obtained in the laboratory through stereoselective synthesis or resolution procedures that separate stereoisomers. In natural products and food contexts, tartaric acid and its salts are more commonly encountered as the D/L pair, while the meso form is less often isolated from natural sources.

Significance: mesotartaric acid is a classic example of a meso compound in stereochemistry, illustrating how two stereocenters with opposite configurations can yield a molecule that is superimposable on its mirror image and therefore non-rotatory in polarized light. It provides a useful contrast to the chiral enantiomers in discussions of chirality and stereoisomerism.