Cahn-Ingold-Prelog system, extension

The specification of configurations in diastereomeric species is quite simple, with each chiral center being designated R or S according to the sequence rules when the Cahn-Ingold-Prelog convention is used. An extension of the Fischer convention to systems with more than one asymmetric center that is based on carbohydrate structures and terminology is still used in relatively simple cases. This convention can be illustrated with the same stereoisomeric 2,3,4-trihydroxybutanals just discussed. The 2R,3R and 25,35 isomers are d- and L-erythrose, respectively. The 25,3/ and 2i ,35 isomers are d- and L-threose, respectively. The Fischer projection formulas are shown below ... 

Systematic names of compounds have been used in many systems to identify and describe their chemical structures. Until recently, however, those names were mere identifiers of the structures and could not be decoded into connection tables. Stereochemical naming schemes have used the Cahn-Ingold-Prelog (CIP) priority system extensively. As it associates a label (R, S, r, s, 0, or E, Z, e, z, see structures 3-5 for some examples) with an atom or bond, it has been used to code stereochemical information as node and edge attributes in standard connection tables. The labels were manually assigned and could be used in canonical numbering methods because their values did not depend on the particular numbering. 

---