## diastereoisomer excess (diastereoisomeric excess)

Also contains definition of: percent diastereoisomer excess
https://doi.org/10.1351/goldbook.D01675
This is defined by analogy with @E02070@, as $$D_{1}- D_{2}$$ [and the percent diastereoisomer excess as $$100\ (D_{1}-D_{2})$$], where the @M03980@ fractions of two @D01679@ in a mixture or the fractional yields of two @D01679@ formed in a reaction are $$D_{1}$$ and $$D_{2}$$ ($$D_{1}+D_{2}=1$$). The term is not applicable if more than two @D01679@ are present. Frequently this term is abbreviated to $$\text{d.e.}$$
See:
diastereoisomerism
,
stereoselectivity
Source:
PAC, 1996, 68, 2193. (Basic terminology of stereochemistry (IUPAC Recommendations 1996)) on page 2205 [Terms] [Paper]