Diastereomeric excess

The diastereomer excess , or de value for short (from English : diastereomeric excess), indicates the excess of a diastereomer in a diastereomer mixture.

It is defined as

${\displaystyle de={\frac {m_{1}-m_{2}}{m_{1}+m_{2}}}\cdot 100\,\%}$

with : mass of the diastereomer in excess,: mass of the diastereomer in deficit. The definition of the diastereomeric excess de is thus similar to that of the enantiomeric excess ee . The characterization of stereoisomeric mixtures with ee and de values ​​is largely obsolete today, as there are the more clearly defined terms enantiomeric ratio er and diastereomeric ratio dr . ${\displaystyle m_{1}}$ ${\displaystyle m_{2}}$

With a 1: 1 mixture of two diastereomers, de = 0%, with a diastereomerically pure compound de = 100%

Nowadays the term diastereomer excess de is increasingly being replaced by the term diastereomeric ratio ( dr ), a mixture of diastereomers being characterized by the ratio [m ₁ ]: [m ₂ ] or [m ₂ ]: [m ₁ ].

For example, with mass fractions of the diastereomers of 70% to 30%, a 40% diastereomer excess (40% de ) results for the diastereomer mixture. The diastereomer ratio in this example would be dr = 7: 3.

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 .

literature

• Y. Izumi, A. Tai: Stereo Differentiating Reactions , Academic P., US, 1977, 343 pages, ISBN 0123778506 , ISBN 978-0123778505