Homotopic, Enantiotopic, and Diastereotopic Systems

It turns out that there are three possible relationships for such geminal groups They can be homotopic, enantiotopic, or diastereotopic. 

Enantiotopic groups are sometimes called prochiral groups. When one or the other of these groups is replaced by a different one, a chiral molecule results. The original molecule is not chiral, but it can produce a chiral molecule. The reaction of prochiral molecules with a chiral reagent, such 

FIGURE 5.58 Replacement tests for homotopic, enantiotopic, and diastereotopic hydrogens. 

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