Imagine substituting H a with, for instance, a methyl group. Then work out the configuration by applying the priority rules. Substitution of a pro-R group will not necessarily lead to a compound with an R configuration. The actual configuration will depend on the incoming group. Topicity Topicity terms refer to the relationship between two specific groups.
Stereoselective reactions distinguish between identical groups of the same connectivity.
These groups can be diastereotopic , enantiotopic or homotopic . Diastereotopic groups Diastereotopic groups cannot be exchanged by any symmetry operations. Any geminal pair in a chiral molecule is diastereotopic. This can frequently be detected by NMR as the groups are in different enviroments. Diastereotopic groups may also occur in molecules that are achiral or which contain symmetry elements unrelated to the pair of groups considered.