Diastereomeric ratio

from Wikipedia, the free encyclopedia

The diastereomeric ratio , or short dr value (of English : diastereomeric ratio), is a modern term used in chemistry , more precisely from the stereochemistry . It is used to characterize a mixture of diastereomers and is increasingly replacing the obsolete term diastereomeric excess de (from English: diastereomeric excess).

A mixture of diastereomers is characterized by the quantitative ratio [diastereomer 1]: [diastereomer 2], it also being possible for the diastereomers to be present as racemates .

Analytics

Chromatographic methods ( gas chromatography or high pressure liquid chromatography ) or nuclear magnetic resonance spectroscopy (NMR) are predominantly used for analysis . These methods allow the concentration of each individual diastereomer to be measured individually in a mixture of diastereomers, without using a chiral stationary phase ( GC , HPLC ) or without adding enantiomerically pure aids (NMR: chiral shift reagents or chiral solvents). The ratio of the integrals of equivalent peaks in the chromatograms or the integrals of equivalent peaks in the NMR spectra is equal to the diastereomer ratio.

Individual evidence

  1. ^ Robert E. Gawley: Do the Terms "% ee" and "% de" Make Sense as Expressions of Stereoisomer Composition or Stereoselectivity? J. Org. Chem. 71 ( 2006 ) 2411-2416; doi : 10.1021 / jo052554w .
  2. ^ Robert E. Gawley: Do the Terms "% ee" and "% de" Make Sense as Expressions of Stereoisomer Composition or Stereoselectivity? J. Org. Chem. 71 ( 2006 ) 2411-2416; doi : 10.1021 / jo052554w .
  3. ^ Ernest L. Eliel, Samuel H. Wilen: Stereochemistry of Organic Compounds , John Wiles & Sons, 1994, pp. 221-240, ISBN 0-471-05446-1 .