Ring system identification

The ring system identification currently implemented in AUTONOM is a two-step process initiated by the ring system perception. The reliability of the ring perception routine is the crux of the naming algorithm. 

Figure 2-36. Identification of the number of rings in adamantane after graph reduction (the different ring systems are highlighted with bold lines). Note that a graph does not car 3D information thus, the two structures on the upper right-hand side are identical.

Although many sterols and bile acids were isolated in the nineteenth century, it was not until the twentieth century that the stmcture of the steroid nucleus was first elucidated (5). X-ray crystallographic data first suggested that the steroid nucleus was a thin, lath-shaped stmcture (6). This perhydro-l,2-cyclopentenophenanthrene ring system was eventually confirmed by the identification of the Diels hydrocarbon [549-88-2] (4) and by the total synthesis of equilenin [517-09-9] (5) (7). 

Geometrical parameters provide much more information than simple identification. The phosphorus-carbon distance of 1.686(6) A in this tungsten complex is consistent with there being a double bond, as it is close to those observed in open chain phosphaalkenes. But how much better it would have been if the parent compound could have been studied uncomplexed, so that the strain in this unusual ring system could have been investigated. The geometrical parameters would then have provided very useful information about the likely reactivity of the compound, and information about the changes on... 

Bohl M, Dunbar JB, Gifford EM, Heritage T, Wild DJ, Willett P, Wilton DJ. (2002) Scaffold Searching Automated Identification of Similar Ring Systems for the Design of Combinatorial Libraries. Quant. Struct.-Act. Rel. 21 590-597. 

GC-MS Analysis. PAHs produce stable molecular ions upon electron impact very little subsequent fragmentation takes place. This is advantageous in determining molecular weight and hence the empirical formula and ring system of a PAH molecule. However, lack of fragmentation makes it usually impossible to differentiate between structural isomers. Chromatographic separation is therefore essential for identification isomeric PAHs by GC-MS. 

Annelation on to a benzene ring increases considerably the complexity of the spectra, and indole has absorptions at 216 (4.54), 266 sh (3.76), 270 (3.77), 276 (3.76), 278 (3.76) and 287 (3.68) nm in ethanol solution. Because of the widespread occurrence of the indole ring system in nature and the sensitivity of absorption band position and intensity to substitution type, considerable use has been made of electronic spectroscopy in the past for structure identification. An extensive tabulation of data, primarily for monosubstituted derivatives, is available (71PMH(3)67,p.94). As expected, whereas the effects of alkylation are comparatively slight, introduction of groups capable of mesomeric interaction with the indole it -system may cause profound changes in the appearance of the spectrum representative examples are given in Table 24. 

A substantial listing of UV spectra of coumarins is available (71PMH(3)190) and examples of the identification of natural products based on the coumarin ring system by UV analysis, amongst other methods, have been reported (58JA3686,69MI22202). 

Highly-colored Jackson-Meisenheimer,or a, complexes of structure II or III are formed by addition to the ring system. The controversial history of the study of these compds has been well reviewed (Refs 44,46,51,70 82). They are formed in aq and anhydrous medium, and with a variety of organic and inorganic nucleophiles. Most of these studies have been made with 1,3,5 -trinitrobenzene rather than TNT, since the absence of a reactive methyl group in the former simplifies product isolation and identification. 

The Prefix Nor Is Used to Denote a Ring System Devoid of Methyl Groups. The Identification Numbers for the Formulas Correspond to Those Used in Later Charts. The Orientations Shown in Column 1 are Only for Ready Recognition of the Corresponding Larger Bicyclic Carbon Skeletons Recommended in Chart 8. 

One of the most important methods for the identification of unsaturated linkages, and a method which has had important consequences in the study of ring systems in general and alkaloids in particular, is the Paal-Skita method of reduction with colloidal metals, in which finely divided palladium or platinum acts as... 

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