Configurations nomenclature for

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. 

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 F. Spande, unpublished).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).

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

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. 

The nomenclature for biaryl, allene, or cyclohexane-type compounds follows a similar rule. Viewed along the axis, the nearer pair of ligands receives the first two positions in the order of preference, and the farther ligands take the third and fourth position. The nomination follows a set of rules similar to those applied in the central chiral system. In this nomination, the end from which the molecule is viewed makes no difference. From whichever end it is viewed, the positions remain the same. Thus, compound 7a has an ( -configuration irrespective of which end it is viewed from. 

This chapter has provided a general introduction to stereochemistry, the nomenclature for chiral systems, the determination of enantiomer composition and the determination of absolute configuration. As the focus of this volume is asymmetric synthesis, the coming chapters provide details of the asymmetric syntheses of different chiral molecules. 

Since the first reaction undoubtedly proceeds with inversion of configuration at sulfur, and since additional experiments demonstrated that the formation of chlorosulfurane 177 from sulfoxide 180 takes place with retention at sulfur, (5>chirality was assigned to (+>177. As for the designation of absolute configuration, Martin and Balthazor (195) proposed a system of nomenclature for optically active pentacoordinate species. 

Figure 3.8 The two enantiomers of a-aminoacids. Here we follow the classic nomenclature of l- and D-aminoacids for indicating the two chiral forms. In terms of the S, R nomenclature, L-aminoacids correspond to the S absolute configuration -except for cystein, which is R.

In the last few years LEED studies of high Miller index or stepped surfaces have become more frequent. Almost all of these studies have been on fee metals, where the atomic structure of these surfaces consists of periodic arrays of terraces and steps. A nomenclature which is more descriptive of the actual surface configuration has been developed for these surfaces, as described in Section III. In Table 5.5 the stepped surface nomenclature for several high Miller index surfaces of fee crystals has been tabulated. In Fig. 5.1 the location of these high Miller index surfaces are shown on the... 

The common nomenclature for di- or oligosaccharides specifies the order of monosaccharide units, the configuration at each anomeric carbon, and the carbon atoms involved in the glycosidic linkage (s). 

For this set of activities let s assume that the first marble we are working with is dark colored. Figure 8.5 shows the three possible distinct distributions for the first marble. We use the same nomenclature for the relative weights of j = 0 and 1 as before. We will not breakdown the j = 0 list to tell whether the marble is in the left sub-box or the right one, we just define a configuration by the total number in each box, summing over the sub-boxes. The results are the same as before W(l, 0) = 2 and W(0, 1) = 1. This time the areas of the boxes did not matter, but the number of sub-boxes in each box (or looking ahead, in each level ) did. We denote the number of sub-boxes in each box j as gj. So, as before, go = 2 and gi = 1 (see Fig. 8.4). 

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 cis and trans nomenclature for alkenes is an old method of classifying the configurational isomers of alkenes and is still in common use. However, it is only suitable for simple 1,2-di-substituted alkenes where we can compare the relative position of the two substituents with respect to each other. When it comes to trisubstituted and tetrasubstituted alkenes, a different nomenclature is needed. 

A later calculation disputed these results in that anti-anti was computed to be the most stable conformer . This work, however, was limited to the SCF level, using a 6-31 -I- -l-G basis set. (If consulting the original paper, it is important to note that this set of workers reversed the standard nomenclature for syn and anti.) Anti-syn was computed to be somewhat less stable, followed by syn-anti and syn-syn. These results were compared to a statistical survey of such interactions in proteins where a marked propensity was observed for the syn-syn structure, the least stable in the gas phase. In contrast, the anti-anti configuration, most stable in the gas phase, is observed rarely in proteins. The authors attributed these discrepancies to crystal packing forces. There also seems to be a preference in the crystals for centrosymmetric (or nearly so) Fl-bonds between carboxyl and carboxy-late, although noncentrosymmetric H-bonds are also present in large numbers. Centrosym-... 

Figure 39-14 Schematic representation of the BCR (22q 11) and ABL (9q34) genes involved in the t(9 22), which is characteristic of all CMLs and a subset of ALLs. The centromeric (cen) and teiomeric (tel) directions are indicated.The relative positions of the major breakpoint duster (M-BCR), the minor breakpoint duster (m-6CR), and the micro breakpoint duster regions (ft-BCR) are shown. The previously used alternative nomenclature for the BCR and ABL exons is included where relevant. In panel A, the exons of the BCR genes are depicted in black rectangles, and those of the ABL genes are depicted in white rectangles. In panel B, the configuration and varieties of the BCR-ABL chimeric fusions seen in CML are shown. In the lower part of panel B, the configuration and varieties of the BCR-ABL fusions seen in ALL are shown. The el-a2 transcript is most commonly detected in t(9 22)-positive ALL, while the b3-a2 and b2-a2 fusions are the most commonly detected in CML...

FIG. 1 Schematic cross sections of selected microelectrode configurations, (a) Nomenclature for parts of microelectrode, (b) Na+-sensitive microelectrode (22), (c) recessed-tip Na+-sensitive microelectrode (27), (d) liquid ion-exchanger micropipette electrode (38), (e) coated wire electrode (16), (f) flow-through ISE (e.g., NOVA 6, Boehringer ISE 2020), (g) micro-capillary glass electrode of tubular shape (e.g., Radelkis OP-266), (h) planar sensor fabricated by microelectronic technology (93), (i) ISFET sensor (94). 

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