Stereoisograms for reorganizing the theoretical foundations of stereochemistry and stereoisomerism. Part 2: rational avoidance of misleading standpoints for R/S-stereodescriptors of the Cahn-Ingold-Prelog system

摘要

The stereoisogram approach presupposes three distinct pairs of attributes, that is, chirality/achirality, RSstereogenicity/ RS-astereogenicity, and sclerality/asclerality, which are integrated into RS-stereoisomerism represented by stereoisograms. The mathematical rationalization of the three pairs of attributes is in sharp contrast to the presumption of a single pair of attributes (i.e., chirality/achirality) supporting modern stereochemistry. Thus, a pair of R/S-stereodescriptors of the Cahn-Ingold-Prelog (CIP) system is clarified to be assigned to a pair of RS-diastereomers, not to a pair of enantiomers. In particular, the ‘units’ of the CIP system (e.g., ‘chirality units’, ‘stereogenic units’, and ‘pseudoasymmetric units’) are replaced by promolecules having type-I, type-III, or type-V stereoisograms; the ‘chirality rule’ of the CIP system is replaced by the RS-stereogenicity rule of the stereoisogram approach; as well as the use of ‘reflection invariance’ for ‘pseudoasymmetric units’ being avoided by developing the concept of chirality faithfulness/unfaithfulness. Global and local symmetries are discussed in terms of correlation diagrams of stereoisograms.