Constitutionally identical atoms or groups in molecules which are related by symmetry
elements of the second kind only (mirror plane,
inversion centre or rotation–reflection axis). For example the two groups
c in a grouping
Cabcc are enantiotopic. Replacement of one of a pair of enantiotopic groups forms one of
a pair of enantiomers. Analogously, if complexation or addition to one of the two
faces defined by a double bond or other molecular plane gives rise to a
chiral species, the two faces are called enantiotopic.
Source:
PAC, 1996, 68, 2193
(Basic terminology of stereochemistry (IUPAC Recommendations 1996))
on page 2207