Formula index systems

Various criticisms (5, 8, J3, 14) of existing formula indexing systems have appeared in the literature. It is beyond the scope of this paper to discuss these at this time. 

The Chemical Abstracts System (CAS) produces a set of various databases ranging from bibliographic to chemical structure and reaction databases. All the databases originate from the printed media of Chemical Abstracts, which was first published in 1907 and is divided into different topics. Author index, general index, chemical structure index, formula index, and index guide arc entries to the corresponding database (Table 5-3). 

The indexing of organic compounds described since 1922 has been taken over by the Chemisches Zentralblatt, which follows the system hitherto discussed. The collective indexes of this journal for 1922 to 1924,1925 to 1929, and 1930 to 1934 continue the classifying work of M. M. Richter. In these indexes the references are to the Zentralblatt itself. Each year of the Zentralblatt, from 1925 onwards, contains a formula index covering the annual increment of literature abstracted in this comprehensively planned journal. These formula indexes are amalgamated every few years into a collective index and individually they constitute the reference works for the period which has elapsed since the appearance of the last collective index. Consequently, when it is desired to have complete information from the whole literature about an organic substance, the following works must be consulted at the present day ... 

Note The formulas in the Inorganic Syntheses, VoL 32 Formula Index fallow the CAS Registry system. 

To facilitate finding all systems containing a given component a formula index is included at the end of the tables listing the systems containing a given component. 

CAS Registry Numbers are included in the printed Chemical Abstracts chemical substance and formula indexes and in the CAS databases. The full set of CAS Chemical Registry System database information—structures, names, formulas, and ring data—is available for search and display through STN International, SciFinder, and other CAS search services. CAS Registry information is also available in CAS databases offered by other online system vendors. 

The Formula Index links the molecular formulae of chemical substances with their CA Index Names, CAS registry numbers, and CA abstract numbers. Molecular formulae are arranged according to the Hill system order (see Section 10.1). 

The Index of Ring Systems was discontinued after the twelfth Collective Index period. For the 1st to the 6th Collective Indexes, Ring System Information was included in the introduction to the Subject Index for the 7th to the 12th Collective Indexes, the Index of Ring Systems was bound with the Formula Index. 

Appendix II Indexes to Chemical Abstracts Organisation and Use is a comprehensive account of the organisation, and relationships, of the CA Chemical Substance Index, CA General Subject Index, CA Formula Index, and CA Index of Ring Systems. This appendix also describes the CAS Chemical Registry System and the criteria applied in selecting CA index entries. 

Although the Hill system is now used almost exclusively, other systems have been used in the past. For example, the early formula indexes to Beilstein used the Richter system, in which the elements are cited in the order C, H, O, N, Cl, Br, I, F, S, R... 

Figure 9.3. MACCS— the Molecular ACCess System—an early structure indexing system. This program originally used fixed menus for searching, registration, and reporting. Later versions allowed users to customize the menus. The figure shows the result of a 3D pharmacophore search for ACE inhibitors. Out of a database of 115,000 structures, 21 fit the 2D and 3D requirements of the search query. The user could typically browse the "hits" from the search, save the list of structures to a list file, and output the structures to a structure-data file (SDFile). The MACCS database was a proprietary flat database system in which data of a given type, say, formula, was stored in a given file, indexed by the compound ID number.

Registry Number, which is unique to each compound, is used to link the structure with names, references, and other information within the Chemical Abstracts Service Registry Number System. However, there is no way to generate a Registry Number from a given structure, and data on specific compounds can only be recovered by finding the Registry Number first. The first formula index to use these numbers will be that for vol. 71 (1969). 

The most useful of these is Beilstein s Handbuch der organische Chemie, which lists the methods of preparation, the reactions, and the properties of all organic compounds which were reprorted in the years that are covered. The main series covers the literature up to 1909, the first supplement covers 1910—1919, and the second supplement covers 1920—1929. A third supplement, which has begun to appear, covers 1930—1949. There is a system which determines where a given compound win appear in the series, but with the advent of subject and formula indexes, there is no longer a need to become familiar with this system. 

Searchers in the chemical field have aids such as subject and formula indexes, classified abstracts, machine codes, and classification systems. Nevertheless trial-and-error prospecting is often necessary to find the shortest path to the goal. This search goal must be clearly conceived and matched with the allowable expenditure. 

There are two systems of formula indexing in common use today, the Hill and the Richter systems. 

The Hill system is used in modified form today by Chemical Abstracts and Referativny Zhurnal, Khimiya (17) and indexes both inorganic and organic compounds. Beilsteins Handbuch (2) formula index to the second supplement uses the Hill system. This index covers the original work and two supplements. 

Certain modifications of the Richter system have been made in Stelzner (21), Beilstein, and Chemisches Zentralblatt (Table I). Unless otherwise stated, the following rules apply to all three formula indexes. Corresponding entries are given for Chemical Abstracts. 

The primary purpose of a formula index is to enable one to locate a single definite compound of which the formula is known. Both of the above systems classify primarily on the basis of C and H. By rearranging the symbols in the formula, such as relegating the C and H to the end of the formula, classification according to the hetero elements (elements other than C) can be accomplished. Whether such classifications are of sufficient value to justify the introduction of additional types of formula indexes is open to debate. Classification on the basis of functional groups and structural features would have some advantages. 

Volumes 28 and 29 of the Second Supplement are, respectively, the subject and formula indexes to the entire "Beilsteins Handbuch the three-part cumulative formula index, arranged by the Hill system, is the only index recording the known formulas of organic compounds from the beginnings of organic chemistry through 1929. (The Chemical Abstracts cumulative formula index extends this period to 1946.)... 

Tri-, tetra- to polycyclic compounds (part B) appear in the structural formula index in order of ring size (carbocyclic before heterocyclic ring compounds) under appropriate compound headings. Part C contains spiro compounds with similar ordering followed by part D which contains assemblies of identical cyclic systems (c.g., bicyclopropyl). 

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