The foundation of the Cahn-Ingold-Prelog (CIP) system has been redefined by employing the concept of RS-stereogenicity derived from stereoisograms for analyzing stereoisomerism, where R-and S-stereodescriptors are pairwise given to two molecules in an RS-diastereomeric relationship. The conventional definitions of RS-stereodescriptors which are based on the original term "chirality" (along with enantiomeric and diastereomeric relationships) and on the revised term "stereogenicity'" are altogether abandoned. Thereby, the present foundation is shown to be distinct from and to be more consistent than the conventional one which assigns R-and S-stereodescriptors to two molecules in an enantiomeric relationship as well as in a diastereomeric relationship. In order to harmonize the present foundation with the conventional one and to leave conventional results unchanged as far as possible, RS-stereodescriptors given originally to a pair of RS-diastereomers are considered to be translated into RS-stereodescriptors for a pair of enantiomers, where the concept of chirality-faithfulness of priority sequences has been proposed to testify whether the translation process of RS-stereodescriptors is faithful or not. As a result, the specification of configurations is rationalized on a more succinct basis than the conventional foundation which emphasizes the dichotomy between enantiomers and diastereomers. A paradigm shift from enantiomers to RS-stereoisomers has been pointed out so that over-simplified features of the conventional dichotomy between enantiomers and diastereomers have been discussed by means of stereoisograms.
The pro-R/pro-S system has been redefined by using the concept of pro-RS-stereogenicity, where two ligands in an RS-diastereotopic relationship are pairwise characterized by pro-R-and proS -descriptors on the basis of stereoisograms. As for a practical criterion for determining RS-diastereotopic relationships, a symmetry criterion has been developed as a new matter by extending the concept of stereoisograms to testify RS-diastereotopic relationships. The conventional definitions of pro-R/pro-S-descriptors which are based on the original term "prochirality" (along with enantiotopic and diastereotopic relationships) and on the revised term "prostereogenicity" (along with stereoheterotopic relationships) are altogether abandoned. The revised concept of prochirality has a purely geometric meaning, which stems from the term enantiotopic relationship or equivalently enantiospheric equivalence class (S. Fujita, Symmetry and Combinatorial Enumeration in Chemistry, Springer-Verlag, Berlin-Heidelberg (1991)). The two concepts for describing intramolecular environments, i.e., the pro-RS-stereogenicity and the prochirality, are clarified to correspond to the concepts of RS-stereogenicity and chirality, which have been formulated on the basis of stereoisograms in order to bring about a harmonized viewpoint to stereoisomeric and geometric intermolecular features of stereochemistry (S. Fujita,
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