Stereochemical nomenclature

Sloan, T. E., Stereochemical Nomenclature and Notation in Inorganic Chemistry, 12, 1. 

The currently used stereochemical nomenclature systems for configurations with four or more ligands are chirality oriented, refering to rigid configurations, or their monocentric subunits. The preceding discussion demonstrates, however, that in many cases it is preferable to use a polycentric representation. 

Scheme 2.1 Kinetic resolution of glycidyl butyrate catalyzed by porcine pancreatic lipase, PPL The preferential conversion of (S)-glycidyl butyrate into (R)-glycidol and butyric acid results from the stereochemical nomenclature rules under the Cahn, Ingold, Prelog convention, the configuration around the chiral centre is not affected.

Pericyclic reactions are described in Chapter 12 as a special case of frontier orbital interactions, that is, following Fukui [1]. However, the stereochemical nomenclature supra-facial and antarafacial and the very useful general component analysis of Woodward and Hoffmann [3] are also introduced here. 

The present discussion of isomerism in coordination compounds is not, nor was it intended to be, comprehensive and exhaustive. The examples considered are an eclectic selection, and many important systems may have been neglected through ignorance. An obvious omission is any detailed consideration of polynuclear complexes139,256"259 and it is, of course, a quite arbitrary decision not to include any consideration of organometallic species. Other neglected issues, such as the development of a truly comprehensive system of stereochemical nomenclature, are perhaps not yet capable of solution. Nevertheless, it is to be hoped that the principal factors to be considered... 

E. L. Eliel, Recent Advances in Stereochemical Nomenclature, J. Chem. Educ. 48, 163 (1971). 

Added in proof) With the recent additions to stereochemical nomenclature lw, it becomes possible to name the faces of compound 62 in rejsi terminology. The cyclobutanone is opened with a double complementation of C(l) yielding (i) in which the left branch has auxiliary descriptor R0, the right S0. The top face is thus si and the bottom face re 178>. 

Stereoisomers among the tetpenes are abundant and exceedingly important to the chemistry of the field. Stereochemical nomenclature therefore cannot be ignored in any complete scheme for systematizing terpene nomenclature for the present, however, the recommendations in this report provide only structural names for the simple acyclic, monocyclic, and bicyclic terpene hydrocarbons. Studies in various fields — e.g., steroids — on preferred methods of designating isomeric configurations are being made by other committees (1, 21, 25). 

The scope of this problem can be indicated by a brief consideration of the stereochemical nomenclature of hydroxy derivatives of the bicyclic terpenes. For the parent bicyclic hydrocarbon compound known in the literature at present as cam-phane, the name "bomane is recommended in this report. (Reasons for choosing "bornane are discussed later under "The Bornane Hydrocarbons .) A mono-hydroxy derivative of bornane, on the basis of IUPAC rules (41), would be named as a bornanol. Two such derivatives have the common terpene names, bomeol and isobomeol these names, on the basis of recommendations in this report would both become 2-bornanol. Obviously, this is inadequate and additional designations are necessary to distinguish between die two stereoisomers. 

The olefinic substrates that are cis-trans isomers are by modern stereochemical nomenclature more generally termed diastereomers. That is, they are stereoisomers that are not enantiomers. The fact that they contain no asymmetric carbons is irrelevant to this classification. 

Figure 6 Structures of the four stereoisomers of sphingosine. Sphingosine has two chiral carbon atoms (C-2 and C-3). The Fischer projection formula of each structure is also shown, with C-1 at the top, to illustrate the D/L and erythro/threo stereochemical nomenclature. C-3 has an erythro orthreo configuration as it relates to C-2, depending on whether the similar groups (amino and hydroxy) are on the same or opposite side of the Fischer projection. D versus L refers to the configuration at C-2 relative to the configuration of D-glyceraldehyde versus L-glyceraldehyde.

The basic problem of this suggestion was that the chirality descriptors obtained by the central procedure are the opposite of those derived from the planar approach. Schlogl consequently changed his stereochemical nomenclature [5,9] and. 

As the enantiomeric a-ferrocenylalkyl carbocations are stable species, a stereochemical nomenclature is desirable. We have made a suggestion that extends the planar approach for 1,2-disubstituted ferrocenes to the adjacent cationic center. 

In addition to the R and S designations, compounds with two chiral centers may also be identified by stereochemical nomenclature that describes the entire system. For example, the erythro and threo nomenclature derived from carbohydrate chemistry may be employed to describe the relative positions of similar groups on each chiral carbon. Thus, the ephedrines are designated as erythro forms since the similar groups (OH and NHCH3) are on the same side of the vertical axis of the Fischer projection, and the pseudo-ephedrines are designated as threo forms since like groups are on opposite sites of the vertical axis of the projection (Fig. 10). 

In the stereochemical nomenclature of coordination compounds, the procedure for assigning priority numbers to the ligating atoms of a mononuclear coordination system is based upon the standard sequence rules developed for chiral carbon compounds (the Cahn, Ingold, Prelog or CIP rules6, see Section IR-9.3.3.2). 

Although we have shown that 4 is chiral, and that it has no stereogenic centre, it is not without symmetry. This is best seen with the aid of a Newman projection of 4, which is shown in 5. A two-fold (C2) axis of symmetry exists as shown this passes through the central carbon, C(2), and bisects the right angle between the two chlorine atoms (and likewise the two hydrogen atoms). Rotation about this axis by 180° gives an identical molecule. Because of the axis of symmetry, 4 cannot be said to be asymmetric, and similar situations are found in certain other chiral molecules. This has had implications for stereochemical nomenclature. In particular, to avoid confusion the term asymmetric carbon is now little used even for an sp3 hybridized carbon that carries four... 

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