Enantiotopic Definition:

Protons that are not interchangeable by rotational symmetry but are interchangeable by reflectional symmetry.

Enantiotopic Explained:

Constitutionally identical atoms or groups in molecules which are related by symmetry elements of the second kind only (mirror plane, inversion center 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.