From: G.P.Moss (G.P.Moss$##$qmw.ac.uk)
Date: Wed May 27 1998 - 12:22:36 EDT
The IUPAC recommended symbol for axial or planar chiral systems is Ra, Sa,
Rp and Sp where the R or S are italic and the a or p are subscripts. See
the IUPAC Basic Terminology of Stereochemistry, Pure Appl Chem 1996, 68,
2193-2222 or on the web at www.chem.qmw.ac.uk/iupac/stereo/
Dr GP Moss Telephone: +44 171 775 3262
Department of Chemistry
Queen Mary & Westfield College Facsimile: +44 181 981 8745
Mile End Road
London E1 4NS, United Kingdom E-mail: g.p.moss$##$qmw.ac.uk
World Wide Web server: http://www.chem.qmw.ac.uk/
IUPAC chemical nomenclature data base: http://www.chem.qmw.ac.uk/iupac/
IUBMB biochemical nomenclature data base: http://www.chem.qmw.ac.uk/iubmb/
On Wed, 27 May 1998, Bob Gawley wrote:
> >HI all,
> >One more theoretical question of mine: Is SBINAP pS-Binap or aS-Binap; for
> >what type of chirality does S stand??
> >Thank you
> They are all the same, sort of...
> Cahn, Ingold, and Prelog (CIP) codified the R,S system in 1966 (Angew
> Chemie Int Ed Engl vol 5, p. 385; Angew Chemie vol 78, p. 413). Prelog and
> Helmchen (PH) modified it slightly and proposed some changes relevant to
> your question in 1982 (Angew Chemie Int Ed Engl v. 21, p. 567; Angew Chemie
> v. 94, p. 614).
> CIP defined R/S to describe (specify) absolute configuration, most usually
> about a chirality CENTER. The prefixes "a" and "p" refer to chirality AXES
> and PLANES. The rules are in the 1966 paper, but the prefixes are often
> omitted in the literature nowadays. It doesn't really matter if you use the
> prefixes, since aS = pS = S.
> I should also point out that PH recommended in the 1982 paper that the
> prefixes P (for Plus) and M (for Minus) could (should) be used in place of
> R/S for chirality axes and planes, and my own experience suggests that it
> is infinitely easier to derive a P/M descriptor for an axis or a plane. Let
> me see if I can produce a diagram that illustrates how easy it is:
> For 1 having higher priority than 2, a chirality axis might look like this,
> viewed along the chirality axis:
> (I intend for the horizontal line to be toward the viewer).
> Now, to proceed from the higher priority ligand in front to the higher
> priority ligand in back, you go clockwise, therefore the configuration is P.
> If you want to convert from P/M to R/S, arrange them alphabetically, then
> equate them vertically:
> R / S
> M / P
> (R=M, P=S).
> For definitions and further details (and better pictures), see pp. 30-31 of
> "Principles of Asymmetric Synthesis" R. E. Gawley and J. Aube, Elsevier:
> Oxford, 1996; or for considerable detail, see Ch. 14 of "Stereochemistry
> of Organic Compounds", E. L. Eliel, S. H. Wilen, L. N. Mander, Wiley: New
> York, 1994.
> Bob Gawley
> Robert E. Gawley, Professor
> Department of Chemistry
> University of Miami
> P. O. Box 249118
> Coral Gables, Florida 33124-0431
> Phone: 305-284-3279
> FAX: 305-668-3313
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