Cahn-Ingold-Prelog rules chiral nomenclature

Scheme 2.1 Kinetic resolution of glycidyl butyrate catalyzed by porcine pancreatic lipase, PPL The preferential conversion of (S)-glycidyl butyrate into (R)-glycidol and butyric acid results from the stereochemical nomenclature rules under the Cahn, Ingold, Prelog convention, the configuration around the chiral centre is not affected.

In the stereochemical nomenclature of coordination compounds, the procedure for assigning priority numbers to the ligating atoms of a mononuclear coordination system is based upon the standard sequence rules developed for chiral carbon compounds (the Cahn, Ingold, Prelog or CIP rules6, see Section IR-9.3.3.2). 

The R and S nomenclature was first presented in 1951 by Cahn and Ingold [26], and then consolidated and extended by Cahn, Ingold and Prelog [27,28]. The essential part of this nomenclature (also called the CIP nomenclature) of chiral centers is the sequence rule, i.e., a set of arbitrary but consistent rules which allow a hierarchical assignment of the substituents (a > b > c > d). 

The sequence rule was introduced by Cahn, Ingold and Prelog (1956) as an aid to nomenclature of optically active molecules. The authors stated that use of the symbols (R) and (S) would remedy ambiguities that arose when the D and L system was applied outside the carbohydrate and amino-acid series. They also claimed that it would systematize the storage of stereochemical information and assist retrieval, e.g. for building a molecular model. The utility of the system is greatest when two or three chiral atoms are present in the same molecule. A simplified version of the sequence rule is presented by Cahn (1964). 

To differentiate two enantiomers, we need a system of nomenclature that indicates the arrangement or configuration of the four groups about the chiral center. Such a system was developed by three chemists, R. S. Cahn, C. Ingold, and V. Prelog. The first step is to rank the four substituents in order of decreasing priority. The rules for assigning priorities will be described shortly. 

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