Alternative nomenclatures are recorded in many cases in Section C, as in Sections A and B. The Commission has attempted to keep the number of alternatives to a minimum. For certain types of compound, however, e.g. azo and hydrazo compounds, Beilstein's Handbuch der organischen Chemie and Chemical Abstracts have practised different but adequate systems of nomenclature. In such cases rules for the systems used by the two groups are presented as alternatives without prejudice. Occasionally other alternatives are included for what seem to be significant reasons. It is recognised that in chemical discussions it may sometimes be necessary to depart from the present rules in order to provide a name more appropriate to the chemical intent or to avoid obscuring an important feature; nevertheless, it is hoped that such deviations from the rules will be made only when necessary and that, at least when the divergence is great, authors will give also the names formed according to the systematic rules.
Many trivial names occur in the rules that follow. Needless creation of new trivial names is discouraged (cf. the Introduction of Sections A and B), and old trivial names which are seldom used should be replaced by systematic ones. If a new trivial name is created, any syllables in it that are used in systematic nomenclature must bear their systematic meaning and be used by the systematic methods.
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