diastereoisomer excess (diastereoisomeric excess) 

Also contains definition of: percent diastereoisomer excess
https://doi.org/10.1351/goldbook.D01675
This is defined by analogy with enantiomer excess, as D1−D2 [and the percent diastereoisomer excess as 100 (D1−D2)], where the mole fractions of two diastereoisomers in a mixture or the fractional yields of two diastereoisomers formed in a reaction are D1 and D2 (D1+D2=1). The term is not applicable if more than two diastereoisomers are present. Frequently this term is abbreviated to d.e.
See: diastereoisomerism, stereoselectivity
Source:
PAC, 1996, 68, 2193. (Basic terminology of stereochemistry (IUPAC Recommendations 1996)) on page 2205 [Terms] [Paper]
Citation: 'diastereoisomer excess' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.D01675 RIS BibTex EndNote
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Last revised: February 24, 2014