Constitutionally equivalent atoms or groups of a molecule which are not symmetry related. Replacement of one of two diastereotopic atoms or groups results in the formation of one of a pair of diastereoisomers. In the example below the two hydrogen atoms of the methylene group C-3 are diastereotopic.
See also: prochirality, enantiotopic, heterotopic
PAC, 1996, 68, 2193 (Basic terminology of stereochemistry (IUPAC Recommendations 1996)) on page 2206