Definition of Diastereotopic

1. 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.