Systematic and Trivial Nomenclature

Nomenclature Notes|A column about the Principles of Chemical Nomenclature—A Guide to IUPAC Recommendations, 2011 EditionSee also www.iupac.org/publications/ci/indexes/nomenclature-notes.html

Systematic and Trivial Nomenclature

by Jeffery Leigh

Nomenclaturists recognize two general classes of nomenclature, systematic and trivial. Perhaps the use of the word trivial is unfortunate, because its usual meaning in every-day English according to the Oxford English Dictionary (OED) is “of small account, little esteemed, paltry, poor, trifling, inconsiderable, unimportant, slight.” However, the OED lists several other meanings, some derived from a Latin word implying “three.” A more general common meaning listed in the OED is “such as met with anywhere, common, commonplace, ordinary, trite.” The word trivial was adopted when nomenclature was in its infancy and when its use in the latter sense was more usual, and that is why it is still used in that sense today. It is not intended to be dismissive.

The traditional names of the elements are trivial in this sense. They are non-systematic and many have been adopted from alchemy and early chemistry. For example, the term mercury was applied to many plants, persons, and things as well as the metal itself, which was also called quicksilver, for obvious reasons. An alternative name, hydrargyrum, from which the symbol Hg was derived, is a compound word from Latin and Greek meaning liquid silver. The reason for such names is very evident, but that can hardly form the basis of a systematic nomenclature for all elements. However, most element names are so deeply embedded in many languages that even IUPAC has refrained from generally systematizing them. Nevertheless, during the 1990s it became clear that many scientists needed to write and speak about elements that had yet to be prepared, and that names and symbols were required. Hence, IUPAC developed names and symbols for such elements that are immediately recognizable and based upon their atomic numbers. These names are provisional and are replaced as soon as a given element is prepared and unequivocally characterized. Perhaps unfortunately, the unambiguous systematic name is then replaced by a trivial name suggested by the scientists who first prepared the element.

Trivial names for compounds are used by chemists everywhere, and such names are clearly useful for much exchange of information, especially within a given lab. However, IUPAC attempts to devise a fully systematic approach to the names of substances, which imply unequivocally their chemical constitutions. Such names should be used when an unambiguous identification of compounds is required, as in scientific documents, international treaties, patents, and legal definitions. This is why IUPAC nomenclature can sometimes appear to be so complicated.

There are other kinds of systematic nomenclature. The Chemical Abstracts Service of the American Chemical Society has its own systematic system, similar to IUPAC’s, and with similar aims, but not identical. Other nomenclatures may be systematic, but in a manner differing from IUPAC’s. For example, ISO lists approved names for pesticides, such as afidopyropen, which should be recognizable by professionally qualified users rather than solely by chemists. Such names should be translatable into other scripts and into languages other than English. The entry for the pesticide afidopyropen (for details see <www.alanwood.net/pesticides>) also lists French and Russian versions of the name, a guide to (British) English pronunciation of the English name, the chemical structure, and full IUPAC and CAS names. The short ISO name is clearly preferable to the IUPAC systematic name for everyday commercial use, though the ISO listing also provides citations of relevant InChIKeys and InChIs.

Similarly, the World Health Organization issues a list of international nonproprietary names for drugs (INNs), which are names devised and classified according to the pharmacological activity of the substance cited. This is also systematic, but is only loosely derived from IUPAC nomenclature. WHO lists proposed INN names together with a structural formula. Details of the listings can be found, for example, in WHO Drug Information, 23(2), 2009, which may be accessed on-line. The names are given in a form of Latin, and then in English, French, and Spanish, with an indication in each language of its claimed activity, its molecular formula, and its CAS registry number. The names listed here are proposed names, and recommended names are listed elsewhere.

These systems are a selection of those available. Many refer back to systematic IUPAC names, but are adapted to specific purposes. Principles offers a brief guide to some of these, together with suitable references for wider consultation.

Jeffery Leigh is the editor and contributing author of Principles of Chemical Nomenclature—A Guide to IUPAC Recommendations, 2011 Edition (RSC 2011, ISBN 978-1-84973-007-5). Leigh is emeritus professor at the University of Sussex and has been active in IUPAC nomenclature since 1973.

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