Configuration , nomenclature

Until some uniform configurational nomenclature for cyclitols has been generally accepted, it would appear safer for authors in this field to specify the nomenclature used in every article, or to indicate configurations by means of formulas. 

The result of this method is consistent with that obtained by using the corresponding Mosher s ester method (Adn = d(/o-ATMA - (s)-atma) (Fig- 1-25). Note that in the method of Mosher s ester, (Ss — Sr) was applied to calculate Ah) i, the difference in the 2ATMA method is only due to the configuration nomenclature difference caused by the CIP rule. 

The (I ,S)-nomenclature still reminds the user of the right and left handed helical pattern arising from Fresnel s 29> interpretation of optical activity. These patterns are characterized by the combination of a translational and a rotational direction. The Ta skeletal symmetry of tetracoordinate systems submits itself to the pictorial models not applicable to other configurational types. The CIP rules may as well be used to define a configurational nomenclature on the basis of the Fischer projection. If one specified that in such a projection of an (R)-... 

Advisory Committee on Configurational Nomenclature, Nomenclature Committee, Divi-... 

Fig. 10. Structures of 3,5-disubstituted pyrrolizidines from dendrobatid and ranid frogs andbufonid toads (31,73,81, and J. W. Daly, H. M. Garraffo, andT. F. Spande, unpublished). Absolute configurations are unknown. It is assumed, based on analogy to other amphibian alkaloids, that n-alkyl side chains are present. The configurational nomenclature for these pyrrolizidines follows the system devised by Sonnet el at. (122) for 3,5-disubstituted indolizi-dines where the H-S and H-8 configurations are related to that at H-3 and are either cis (Z) or trans (E).

Fig. II. Structures of 3,5-disubstituted indolizidines from amphibians. The absolute configuration of natural levorotatory (S ,9 )-223AB, (5 .9 )-239AB, and (5 .9 )-239CD, are known. Natural dextrorotatory (S ,9 )-195B has the opposite absolute configuration as that shown above U29a). The configurational nomenclature is based on that introduced by Sonnet et at. (122), where the H-S and H-9 configurations are related to that of H-3 and are either cis (Z) or trans ( ).

Identify what appears to be the compound s central molecular scaffold and estimate how flexible or inflexible that system may be in terms of adopting different shapes or movements in 3D space locate any asymmetric centers and if stereochemical information is displayed in the structure then discern the R or S absolute configuration nomenclature for each of these sites. 

The use of S and R to specify the absolute configuration at a dissymmetric carbon atom is a fairly recent innovation (Cahn et al., 1956). This system depends upon no particular orientation of a projection formula, as does D and l configurational nomenclature, yet it unambiguously describes the three-dimensional representation of a dissymmetric atom. 

The experimental observations may, therefore, be rationalized by assuming that the 72-DNDBCH-6-one will have a higher initial rate of reduction. As a result, incomplete reduction of RS-DNDBCH-6-one would be expected to yield a mixture of DNDBCH-6-ol enriched in R enantiomer. The unreacted DNDBCH-6-one should be enriched in S enantiomer. Therefore, (—)-alcohol and (—)-ketone may be assigned the R configuration (for a discussion of the application of R and S configurational nomenclature to biphenyls, see Cahn et al, 1956). The (-f)-alco-... 

See Report of the Advisory Committee on Configurational Nomenclature, pamphlet available from Chemical Abstracts, Columbus, Ohio (1954). Examples of this nomenclature are found, inter aliay in G. E. McCasland and E. C. Horswill, J. Am. Chem. Soc. 75, 4020 (1953). 

Configurations The Kahn-ingold-Prelog System of Configurational Nomenclature... 

The priority rules we defined in Chapter 5 for describing the configuration of geometric isomers also apply to R,S configurational nomenclature for chiral compounds. 

The same nomenclature has been adopted for amino-acids, the configurational family to which the a-carbon atom belongs being denoted by the prefixes d- and L-. 

The next sections describe briefly the nomenclature of configurational isomers, and how this stereochemistry can be handled by computer. 

Only some of the configurations that commonly occur in low power gas lasers are described herein. The modes are denoted by the nomenclature TEM where the term TEM stands for transverse electromagnetic, and where m and n are small integers. Eigure 3 shows some TEM modes that are... 

Implicit ia the base names are the absolute configurations at carbons 8 and 12 and the iadicated numbering systems. Derivatives of these parent stmctures are named according to terpene and steroid nomenclature rules (see Steroids Terpenoids). The lengthy and awkward nature of the chemical abstract systematic nomenclature (12) for these compounds has resulted ia the development (13) and use of simplified nomenclature based on common names. 

The Tubular Exchanger Manufacturers Assn, has established heat exchanger standards and nomenclature. Every shell-and-tube device has a three-letter designation the letters refer to the specific type of stationary head at the front end, the shell type, and the rear-end head type, respectively (a fully illustrated description can be found in the TEMA standards). Common TEMA designations are listed with specific configurations described below. 

Protonation of the anion [SN2] by acetic acid in diethyl ether produces the thermally unstable sulfur diimide S(NH)2. Like all sulfur diimides, the parent compound S(NH)2 can exist as three isomers (Scheme 5.5). Ab initio molecular orbital calculations indicate that the (cis,cis) configuration is somewhat more stable than the (cis,trans) isomer, while the (trans,trans) isomer is expected to possess considerably higher energy. The alternative syn,anti or E,Z nomenclatures may also be used to describe these isomers. The structures of organic derivatives S(NR)2 (R = alkyl, aryl) are discussed in Section 10.4.2. 

The newer (R,S) system of nomenclature is superior to the older d,l system in one important way. The configuration of molecules with more than one... 

Aldoses with at least three carbons and ketoses with at least four carbons contain chiral centers (Chapter 4). The nomenclature for such molecules must specify the configuration about each asymmetric center, and drawings of these molecules must be based on a system that clearly specifies these configurations. 

A system of nomenclature has been devised to describe optical isomers conveniently. These isomers differ in configuration and we have to be able to specify the configuration at the asymmetric atom unambiguously. 

What Do We Need to Know Already This chapter assumes that we know about atomic structure and electron configurations (Chapter 1), the basic features of energy, and the nature of the Coulomb interaction between charges (Section A). It is also helpful to be familiar with the nomenclature of compounds (Section D) and oxidation numbers (Section K). 

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