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.
Source:
PAC, 1996, 68, 2193
(Basic terminology of stereochemistry (IUPAC Recommendations 1996))
on page 2206
