Definition of stereoselectivity, stereoselective

1. Stereoselectivity is the preferential formation in a chemical reaction of one stereoisomer over another. When the stereoisomers are enantiomers, the phenomenon is called enantioselectivity and is quantitatively expressed by the enantiomer excess; when they are diastereoisomers, it is called diastereoselectivity and is quantitatively expressed by the diastereomer excess. Reactions are termed (100%) stereoselective if the discrimination is complete or partially (x%) stereoselective if one product predominates. The discrimination may also be referred to semiquantitatively as high or low stereoselectivity. ELIEL (1962); IUPAC STEREOCHEMICAL TERMINOLOGY (1993).