Term: diastereoisomer excess (diastereoisomeric excess)
https://doi.org/10.1351/goldbook.D01675

Definition:
This is defined by analogy with enantiomeric 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.

Related Terms:
1) enantiomeric excess (http://doi.org/10.1351/goldbook.E02070).
2) mole (http://doi.org/10.1351/goldbook.M03980).
3) diastereoisomerism (http://doi.org/10.1351/goldbook.D01679).
4) stereoselectivity (http://doi.org/10.1351/goldbook.S05991).

Source: PAC, 1996, 68, 2193. 'Basic terminology of stereochemistry (IUPAC Recommendations 1996)' on page 2205 (https://doi.org/10.1351/pac199668122193)

Citation: 'diastereoisomer excess (diastereoisomeric 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

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