Leffingwell Reports, Vol. 3 (No. 1), May 2003


 Following Kekule’s avowal in 1858 that carbon has a valence of 4 [7], vant’ Hoff and Le Bel independently recognized that whenever four different groups are attached to a carbon tittle, arrayed at the corners of a tetrahedron, therefore the arrangements can be in couple different forms, as depicted schematically greater than .As the number of carbons with asymmetry (chirality) increase in a molecule the number of possible optical isomer pairs (enantiomers) too increases. With one asymmetric carbon, 2 isomers (unit pair of enantiomers)…with two asymmetric carbons, 4 isomers (sum of ~ units pairs of enantiomers), with three asymmetric carbons, 8 isomers (four pairs of enantiomers) …that is, the number of stereoisomers is 2


, at what place n = number of asymmetric atoms. Note that in newly come years the term asymmetric is at a past period referred to as “stereogenic”. In the in good season days, chemists often assigned trivial names to differentiate isomers, and enantiomers in general were specified by d- = dextrorotary and l- = leavorotary based without ceasing which direction the molecules polarized etc (not to be confused with the “capital” L- and D- prefixes used according to carbohydrates and amino acids, i.e. Fischer Projection Formulas). But Cahn, Ingold and Prelog [8]


devised a body based on assigning sequence rules based adhering decreasing atomic number (and respective degree of substitution for atoms of the similar atomic number) for projection formulas that allows the

self-determined configuration

 assignments of

 (towards rectus, Latin for right) and


 (as antidote to sinister, Latin for left). These rules are incorporated in the chirality overseer of Accelrys DS Viewer and DS ViewerLite software (the recent being freeware). Very occasionally, DS Viewer provides incorrect assignments (for example, with the enantiomers of gamma-dihydroionone, gamma-damascone & gamma-ionone). However, Cambridgesoft’s ChemDraw Ultra appears to procure essentially 100% correct C-I-P (R-, S-) assignments. Thus, unruffled without knowing the Cahn, Ingold and Prelog


following rules, chemist’s today can swiftly establish the R/S configuration at reaped ground asymmetric atom for a given corpuscular structure (of known absolute configuration) in good a few minutes.

Chirality & Bioactivity

Most chemists are too free with the role of chirality attached odorants such as (4S)-(+)-carvone, which has a distinct caraway odor, during the time that compared to (4R)-(-)-carvone which has a characteristically harmonious spearmint odor [9].







(4S)-(+)-carvone (4R)-(-)-carvone

Caraway redolence Spearmint odor

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