Ring systems, index

Chemical Abstracts (CA) consists of two main parts, abstracts of every paper containing new chemical information, and indexes which provide access to the abstracts and thence to the original literature. It is published weekly and each issue contains a keyword index and an author index. The weekly issues are collected in volumes covering a six month period (one year, prior to 1962) and each volume contains author, chemical substance, formula, general subject, patent, and ring system indexes. Every five years (ten years, prior to 1957) the indexes for the ten volumes are combined to give Collective Indexes. These indexes are the single most important and comprehensive information tool available to the chemist... 

Index entries are divided into two categories, primary and secondary. Primary index entries are used when a significant part of the text is devoted to a particular ring system this may be a whole chapter, or a section or subsection. Secondary index entries are used when a heterocyclic system is mentioned in a chapter devoted to another (primary) system. This may be, for example, as a starting material or as a product, or in a discussion comparing properties. 

Along with each index (annual, semiannual, or collective) appears an index of ring systems. This valuable index enables the user to ascertain immediately if any ring system appears in the corresponding subject or chemical substance index and under what names. Eor example, someone wishing to determine whether any compounds containing this ring system... 

This index lists the heterocyclic parent ring systems and has been compiled from the occurrences of those systems and their derivatives in Volumes 1-15 in the text, tables, equations, and schemes. Heterocycles have been included when they occur as a starting material, isolable intermediate, or a product, but not when they are reported as a nonisolable intermediate or a solvent. 

There are little data on theoretical chemistry associated with such ring systems. In a series of 5,5-fused heterocycles, the inner salt 1 displays a substantial aromatic character as indicated by the aromaticity index 7(5,5) with a value of 82 <1987T4725>. 

Quinophthalone (6.229) and its derivatives [86] also fall into the methine category, although they appear in the Colour Index under quinoline colouring matters. The parent compound was discovered in 1882 by Jacobsen, who condensed 2-methylquinoline (quinaldine) with phthalic anhydride. The product, quinoline yellow, is used as a solvent dye (Cl Solvent Yellow 33). The light fastness is improved by the presence of a hydroxy group in the quinoline ring system. Derivatives of this type provide greenish yellow disperse dyes for polyester. The moderate sublimation fastness of Cl Disperse Yellow 54 (6.230 R = H) is improved by the introduction of an adjacent bromine atom in Cl Disperse Yellow 64 (6.230 R = Br). 

An appendix systematically lists references to reactions of dialkylalkoxy-malonates with amines, including not only the common aliphatic and aromatic amines, but also a very wide variety of heterocyclic amines classified according to ring system. The appendix also provides systematic references to the different ring systems obtained by ring closure of the dialkylaminomethylenemalonates. The appendix should be used in conjunction with the subject index a separate subject index is provided for this monograph volume. 

Last but not least, the thianthrenes, derived from a ring system that is rapidly increasing in importance because of its electronic properties, are reviewed by Joule. Readers are reminded that this volume will contain no index. The last index volume was Volume 46, and we now plan to designate every fifth volume an index volume thus the next will be Volume 51. 

Fig. 1. Empiric observation that more than approx 20 compounds from any scaffold need to be tested in order to be sure that an active will be found. (A) This shows the results from a whole cell assay in which the compounds have been classified using the Level 1 Ring System of the Structural Browsing Index (SBI) also known as molecular equivalence numbers or meqnums, which is the most-detailed level. The most-populated SBI containing only inactives is labeled 1, it contains 16 compounds. The most populated SBI containing actives is labeled 2. (B) Looking at only the compounds present in the most-populated SBI (2 above) and arranging the compounds in this SBI randomly, the smallest set of compounds in which an active (indicated by +) can be found is approx 30 compounds.

The peak with the parent ion of m/e 226 was assigned benzo[ghi]flu granthene. The reference standard was not available, but its retention index was in agreement with that reported (389.6) by Lee et al. (6). The presence of benzo[b,j k]fluoranthenes was also confirmed. They appeared as one broad peak, but the presence of all three was established by their GC retention time in the HPLC subfraction S1-C2C. Benzo[ejpyrene and benzo[a]pyrene were also characterized by MS. PAHs with higher ring systems were not detected in this sample. 

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). 

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