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Meso compound

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A meso compound or meso isomer is a chemical compound whose molecules contain 2 or more asymmetric atoms (stereocenters) but it is optically inactive (or achiral) because it contains an internal plane of symmetry.

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For example one of the isomers of tartaric acid depicted below is a meso compound. An internal mirror plane exists bisecting the molecule; on rotating the molecule 180° on a plane perpendicular to the screen (that is, superposing the bottom OH with the top one), the same apparent stereochemistry is obtained. (see Fischer projection.)

For a compound with multiple asymmetric carbons, the presence of an internal plane of symmetry indicates that the compound is achiral. However, it is still possible for a compound with multiple asymmetric carbons and no internal plane of symmetry to be meso.

v • d • e Concepts in asymmetric synthesis
Nomenclature	Chirality, Stereocenter, Stereoisomer, Enantiomer, Diastereomer, Meso compound, Planar chirality, Chiral ligand, Axial chirality
Analysis	Optical rotation, Enantiomeric excess, Diastereomeric excess, Chiral derivitizing agents
Chiral resolution	Crystallization, Kinetic resolution, Chiral column chromatography
Reactions	Asymmetric induction, Chiral pool synthesis, Chiral auxiliaries, Asymmetric catalytic reduction, Asymmetric catalytic oxidation, Organocatalysis, Biocatalysis