meso connection
Meso connection is a term from stereochemistry and describes the special case of a molecule that has stereocenters but is still achiral . The exact definition is “meso forms have two (or more even-numbered ) stereogenic centers; and they can exist in at least one conformation which has a c s symmetry ( rotating mirror axis or mirror plane or point symmetry ). "
The prefix meso - according to the definition, is also used as a descriptor in semi-systematic substance names.
Although the presence of stereocenters (e.g. asymmetrically substituted carbon atom) is a frequent cause of the chirality of a molecule, this does not necessarily have to be the case: If the molecule still has a mirror plane (or rotating mirror axis ) in an energetically possible conformation , it behaves macroscopically like an achiral compound. The meso -tartaric acid contains two stereocenters of opposite configuration with the same substituents on each stereocenter:
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In the picture above, all three possible (and existing) isomers of tartaric acid are shown. At the top are the ( S , S ) and ( R , R ) forms. These isomers are chiral and behave like an object and a mirror image; are therefore enantiomeric to each other. The meso form shown below has an intramolecular plane of symmetry between carbon atoms 2 and 3, so it is achiral. In total there are only three isomers of tartaric acid , the two enantiomers and the meso form. In the meso form, one of the stereocenters is ( R ) - the other ( S ) -configured .
Individual evidence
- ↑ Bernhard Testa: Fundamentals of Organic Stereochemistry , Verlag Chemie, Weinheim, 1983, pp. 54–56, ISBN 3-527-25935-X .