Configurational descriptor system

The diirality of a molecule is described by specifying its configuration. The system that is used is the Cahn Ingold-Prel6g convention, which uses the descriptors R and S. The Fischer convention, employing the descriptors D and L, is historically important and is still used with certain types of molecules. 

In retrospect, it was a consistent and logical step for Seebach and Prelog to propose, in 1982 2 a reactant-based descriptor system (SP system) corresponding to the Izumi -Tai classification. The SP system makes use of the familiar Re Si system already discussed (see Section 1.1.2.2.). Again, relative configurational relationships must be incorporated, something which the SP system does by straightforward combination of descriptors into Ikjul pairs (relative topicities) (see Section 1.1.2.2. and 1.1.4.). 

I shall use the configurational descriptors ci5 and trans with the 0" or group always being the point of reference. In the E-Z system, depending on the nature of R, either OM (0 ) or R may be fiducial, which is confusing. 

Assessing stereoselectivity in terms of descriptors is very simple as it merely involves the CIP specification of absolute and/or relative configurations of the stereoisomeric products of a reaction. This is just the task for which the CIP system was developed. The addendum of extraction of relative configuration by the like/ unlike (// ) description1 is explained in Section 1.1.8.1. 

There are several conventions to indicate the configuration of a stereocenter. The most precise is the IUPAC system that names the configuration around a stereocenter as R (for right handed rectus) or S (for left handed sinister). You have probably seen the R/S descriptors on drug information sheets. The details of the R/S system are beyond our purposes here, but any standard organic chemistry text will discuss how to assign these descriptors. 

In the cyclic systems, more commonly observed in the cyclodextrin hydrates, all three alternatives, 1, 2, 3, are expanded to correspond to the configurations 5, 6, and 7, for which the descriptors homodromic, 5, antidromic, 6, and heterodromic, 7, have been applied3 [109], which can also be used for the description of linear... 

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