Ring index, Chemical Abstracts

Conventional Terpene Baeyer-Type Recommended For Adoption Ring Index Chemical Abstracts... 

For single rings (i.e. mononuclear systems) up to ten atoms in size, there is no question but that Hantzsch-Widman names are overwhelmingly the most widely used, and specialists can be presumed to recognize them readily. However, when one of the trivial names of Table 1 can be used, it prevails almost exclusively. Thiophene will be immediately understood by specialists and most nonspecialists, whereas thiole will distract the reader s attention from the chemistry while he considers the writer s intention is the Hantzsch-Widman system indeed being used, or is it a typographical error Chemical Abstracts also uses these trivial names in its indexes. 

According to the systematic nomenclature these substances were first named l-f-triazolo[d] pyrimidines in compliance with the general principles of the Ring Index/ More recent papers and Chemical Abstracts indexes use the term i -triazolo[4,5-d]pyrimidine (147) in accord with the lUPAC nomenclature. The numbering of substituents when using the last-mentioned name is different from that of the 8-aza analogs. For the formulas of oxygen and sulfur derivatives names derived from the lactim or thiolactim form are almost exclusively in use (in common with the purine derivatives). These derivatives are thus described as hydroxy and mercapto derivatives, respectively. The name 1,2,3,4,6-pentaazaindene is used only rarely for this system. 

According to the Ring Index, the system is classified as pyrido-indole and numbered as in 6 (harmine = 7-methoxy-1-methyl-9 -pyrido[3,4-fc]indole). This is the nomenclature adopted by Chemical Abstracts, according to which a-carboline (5) is 9 -pyrido[2,3-6]indole, jS-carboline (6) is 9jy-pyrido[3,4-6]indole, y-carboline (7) is pyrido[4,3-6]indole, and S-carbohne (8) is 5jy-pyrido[3,2-fc]indole. 

The overall style follows that used in Chemical Abstracts and the first two editions of Comprehensive Heterocyclic Chemistry, but in order to keep the size of the index within reasonable bounds more attention has been paid to the monocyclic and bicyclic rings and only systems containing up to six fused rings have been included. For the same reason a limit on individual ring size in any system has been placed at 12 atoms. Also complexes of metals, clusters and carcass structures are not included. 

The nomenclature used in this section differs from the strictly systematic rules used by Chemical Abstracts to index fused-ring azetidinones, but conforms more to that commonly found in the literature describing the /3-lactam antibiotics. A description of this naming system is given in the introduction (Section 5.12.1). Virtually all of the compounds discussed in this section contain a carboxyl group adjacent to the /3-lactam ring and conform to general structure (49). 

In 1928, A. M. Patterson, later one of the authors of the Ring Index, wrote Any attempt to construct a strictly logical system of names for the large number of parent ring systems now known seems impractical, at least as far as common use is concerned. 7 This sentiment is no less applicable today. For heterocycles in particular, the number of trivial names in current use is large. In the 1969 IUPAC Rules,6 63 trivially named heterocyclic skeletons with various degrees of unsaturation are listed, with a further 25 in the 1973 Tentative Rules (Section D).8 Chemical Abstracts nomenclature rules list 83 such skeletons with maximum unsaturation, many of which are not included by IUPAC. Thus, although systematic operations are often required to derive the name of a heterocyclic skeleton, the parent names to which these operations are applied are frequently trivial. 

Although all alkaloids can be named by the principles already outlined in this article, the cumbersome nature of such names for complex ring systems makes it desirable to use trivial parent names for some large heterocyclic skeletons. It is preferable for such trivial names to refer to skeletons with no substituents (or very few), and it is often convenient for them to carry inherent stereochemical implications. The most extensive source of these names is the Chemical Abstracts Index Guide (or the Ninth Collective Index Nomenclature Manual), but the names given here do not correspond, in many cases, to those in common use, and IUPAC recommendations, when they appear, may well differ in some respects. Some of the principal skeletons listed by Chemical Abstracts are illustrated (122-130). 

Heterocyclic systems can be named by various methods, depending on ring size, the presence or absence of metal atoms, the availability of trivial names, etc. For this index the naming of the heterocyclic parents has generally followed the practices of IUPAC and Chemical Abstracts. Thus Hantzsch-Widman names have been employed for all monocyclic systems and for the other systems when the smallest ring size is five atoms or more, but replacement nomenclature has usually been followed for bicyclic and higher systems when they contain three- and four-membered rings. 

This chapter covers the primary chemical literature of the title bi- and tricyclic ring systems cited in Chemical Abstracts Chemical Substance Indexes up to Volume 151 from Volume 144 between 2006 and 2009. Earlier literature data were systematically treated as primary subjects in Comprehensive Heterocyclic Chemistry series (96CHC-II(8)563,08CHC-III(12)77). 

Of the two ring-numbering systems in use for phenanthridine,(l) is favored by Chemical Abstracts, the Ring Index , and the Chemical Society and will be used here. The older alternative (2) is encountered less frequently. 

Although these names are the ones preferred by Chemical Abstracts and the Ring Index, other names have also been used thus, 1 has been described as benz [d]isothiazole or thioindoxazene, and 2 as benz[c]isothiazole or thioanthranil. 

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