Specification of Absolute and Relative Configuration

Compounds with Stereogenic (Traditionally Asymmetric) Carbon (and Analogous) Centers 

For most of the practically important cases the first three criteria are sufficient for assigning conclusive priorities. 

To visualize the stereochemical relationships in tetrahedral molecules the following graphical conventions have been established, among which can be freely chosen according to personal gusto. 

When several stereogenic (formerly asymmetric or chiral) centers are present in a molecule the over-all configuration is characterized by a set of RyS symbols preceding the compound name. 

If only relative confiigurations should be marked the descriptors R IS are applied for both enantiomers in such a way that the center with the lowest locant is arbitrarily labelled with R. Alternatively the unstarred symbols RIS can be utilized here too when specified by the prefix rel 

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