RS Systems

Given the importance of stereochemistry in reactions between biomolecules (see below), biochemists must name and represent the structure of each biomolecule so that its stereochemistry is unambiguous. For compounds with more than one chiral center, the most useful system of nomenclature is the RS system. In this system, each group attached to a chiral carbon is assigned a priority. The priorities of some common substituents are... 

RGURE 1 Pasteur separated crystals of two stereoisomers of tartaric acid and showed that solutions of the separated forms rotated polarized light to the same extent but in opposite directions. These dextrorotatory and levorotatory forms were later shown to be the (R,R) and (S,S) isomers represented here. The RS system of nomenclature is explained in the text. 

In living organisms, chiral molecules are usually present in only one of their chiral forms. For example, the amino acids in proteins occur only as their l isomers glucose occurs only as its D isomer. (The conventions for naming stereoisomers of the amino acids are described in Chapter 3 those for sugars, in Chapter 7 the RS system, described above, is the most useful for some biomolecules.) In contrast, when a compound with an asymmetric carbon atom is chemically synthesized in the laboratory, the reaction usually pro-... 

A clear description of the RS system for naming stereoisomers, with practical suggestions for determining and remembering the handedness of isomers. 

Another system of specifying configuration around a chiral center is the RS system, which is used in the systematic nomenclature of organic chemistry and describes more precisely the configuration of molecules with more than one chiral center (see p. 18). 

Answer A chiral center, or chiral carbon, is a carbon atom that is bonded to four different groups. A molecule with a single chiral center has two enantiomers, designated D and L (or in the RS system, S and) ). In isoproterenol, only one carbon (asterisk) has four different groups around it this is the chiral center ... 

Naming Lipid Stereoisomers The two compounds below are stereoisomers of carvone with quite different properties the one on the left smells like spearmint, and that on the right, like caraway. Name the compounds using the RS system. 

Association effects clearly vary widely in magnitude from one substance to another. As with electrolytes in solution, the nonionic terms in the potential function for interaction may be critically important. Bloem s detailed analysis of equilibria in the Pb1 (rS system shows that although the total stoichiometric defect... 

A-2. Specify the configuration of each stereogenic carbon in the preceding problem, using the Cahn-Ingold-Prelog RS system. 

Configurations may be described by either the dl or the RS system. The older DL system is only useful for chiral centers of the type R—CHX—R. The newer RS system, on the other hand, may be used with any desired chiral center, as well as the chiral axes and chiral planes. 

The RS system is based on purely topological considerations and is consequently independent of reference substances. The individual ligands of a chiral center are ordered according to a sequence in this system whereby the assignment of R- or S- can be derived from the order. The ligands are given different seniorities in the system such that the position in the periodic system of the atom bonded directly to the chirality center determines the seniorities ... 

Finally, the above redox data and the fact that disulfides are oxidized by R2S (and possibly by (R2SaSR2)" ), while (RSSR) ", on the other hand, readily oxidizes RS allow reasonable extrapolations of the reduction potentials of the [R2S (R2S.%SR2)1/R2S (> 1.45 V) and RS7[RSH, RS ] systems (< 1.0 V), with both values being in good agreement with other determinations. 

Fig. 20.12. Electronic structure of the B, M and B-phases in the Smi xGd rS system. The spin-orbit splitting of the 4f level is shown and this is about 35meV. The dashed line shows the Fermi distribution function (from Jayaraman et al., 1975a).

The USPS is exploring the feasibility of AS/RS systems for staging mail pieces between processes. Both a centralized and distributed storage approach are planned. The distributed system has a higher system reliability, and provides storage at the point of use, but the capacity is limited. 

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