• Stereochemical nomenclature;
  • Asymmetric synthesis;
  • Stereochemistry;
  • Nomenclature


The nomenclature of organic chemistry has not kept pace with the staggering advances made in asymmetric syntheses over the last 15 years. Efforts to specify the steric course of stereoselective reactions by use of the terms erythro and threo, and by other descriptors have led to ambiguous notation and consequently to an almost Babylonic confusion. We propose here a method, based on the CIP-(Cahn-Ingold-Prelog) system, for the unambiguous specification of the steric course and the product configuration of diastereoselective reactions. The reflection-invariant relative topicity of approach of reactants is defined as like (lk) and unlike (ul) if the corresponding descriptor pairs are Re*, Re*. or R*, Re*, and Re*, Si*, or R*, Si*, respectively. The descriptor pair notations (lk and ul) of reactants disclose related steric courses of reactions more often than do the relative configurations of their products, for which the configurational notation l=R*, R* and u=R*, S* is proposed. The advantage of specifying the relative topicity is demonstrated by means of a series of recent examples of importance to the synthetic organic chemist taken from the literature and from our own work.