Meso compound

Meso compound is a term from the stereochemistry and refers to the special case of a molecule that has stereocenters, but is nevertheless achiral. The exact definition is " meso forms two (or more even-numbered ), stereogenic centers; and they may be present in at least one conformation which has a Cs symmetry ( mirror axis of rotation or mirror plane or point of symmetry). "

The prefix of the meso- definition is used accordingly as a descriptor in semi- systematic names of substances.

Although the presence of stereocenters (eg asymmetrically substituted carbon atom) is a common cause for the chirality of a molecule, this must be the case not mandatory: If the molecule is still in an energetically feasible conformation on a mirror plane (or alternating axis ) behaves it macroscopically like an achiral compound. Meso -tartaric acid contains two stereogenic centers of opposite configuration with the same substituents at each stereocenter:

It shows all three isomers, all there is. Above are the (S, S) - and (R, R)-form. These isomers are chiral and behave like object and mirror image; are therefore each other enantiomer. Shown below the meso form has an intramolecular plane of symmetry between the carbon atoms 2 and 3, it is thus achiral. Overall, there are therefore three isomers of tartaric acid, the two enantiomers and the meso- form. In the meso- form of the stereo centers (R) - and the other ( S) configuration.