Richter Formula index system

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 ... 

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... 

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

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 formula index, which includes only organic formulae, used the Richter system until 1956. Under this compounds are arranged by the number of carbon atoms they contain and then by the number of other elements in the molecule besides carbon in the... 

The arrangement of formulas within the index by the Richter system may be termed a semiclassified order, depending on ... 

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