The reflection invariance problems in stereochemical nomenclature for absolute configuration

Abstract

Abstract Genesis of chirality and its link to the origin of life continue to intrigue scientists. Chirality also plays an important role in medicine with the advent of chiral drugs and the consequent importance of asymmetric synthesis. The configuration of a chiral molecule gets inverted in its mirror image, as is manifested by (i) sign of specific rotation and (ii) normally, through the absolute configurational notation (R/S). While the first parameter is always true, the second one, that is the mirror image relationship of R and S configurations, called the reflection variance, may not always hold good. In this manuscript, we have highlighted examples of molecules with combinations of central and axial or planar chirality where the mirror image relationship between R and S configurations does not hold. This reflection invariance originates from the CIP rule of R precedes S. Similar reflection invariance can be observed in P or M forms of conformations of some particular molecules with chiral ligands. Proposal to avoid such reflection invariances, has been put forward. An ignorance about the possibility of reflection invariance in enantiomeric molecules can lead to common mistakes about stereoisomeric relationship or reactivity profile.