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Vol. 34 No. 4
July-August 2012

Nomenclature Notes | A column about the Principles of Chemical Nomenclature—A Guide to IUPAC Recommendations, 2011 Edition

Non-IUPAC Nomenclature Systems

In the second "Nomenclature Notes" (May-June 2012 CI, p. 28) we alluded to various kinds of nomenclature that fall under the aegis of IUPAC. There are other nomenclatures in wide use, to some of which IUPAC contributes. For example, biochemical nomenclature is reviewed regularly by a committee which has joint membership from both IUPAC and IUBMB (International Union of Biochemistry and Molecular Biology). It is fair to say that biologists and biochemists are often not interested in systematic nomenclature in the way that chemists are. For them it may be sufficient that a given name is specific and defined so as to make the compound to which it refers unequivocally and universally recognized within the discipline. The IUPAC requirement that a name should convey the structure of a compound is not necessary or even desirable, as long as all practitioners accept it. For example, the compound

may receive a perfectly good IUPAC name, 2,3,4,5-tetrahydroxypentanal, but this might not be recognizable to biochemists unless the compound were named as a sugar, specifically an open-chain form of ribose. As this molecule also contains three chirality centers (asymmetric carbon atoms) to which are assigned the locants 2, 3, and 4, a more complete name would be (2R*,3R*,4R*)-2,3,4,5-tetrahydroxypentanal. Biochemists would also prefer to know the absolute configuration at carbon atom 4, representing it by small capital letters, either D or L, and they would be very comfortable with a name such as D-ribose. When even more complex structures are considered, such as amino acids, steroids, and proteins, the use of defined but semisystematic names becomes necessary for ease of communication and comprehension in biochemical and biological contexts.

A system of nomenclature which is independent of IUPAC, but which is widely used by chemists, is due to the Chemical Abstracts Service (CAS) of the American Chemical Society. This has been developed to produce names for CAS use in both running text and indexes. Although nomenclaturists of CAS have contributed substantially to IUPAC, they cannot afford the leisurely contemplation of data in which IUPAC indulges. They have to make decisions rapidly to meet publication deadlines, and CAS names are designed to be adaptable for use in indexes. Because an index compiler would wish to locate all derivatives of, say, the parent compound butane, at the same place in the alphabetical index, CAS names are sometimes termed "inverted," because, in this specific case in an index the parent name butane would always be cited first. In its Index Guide, CAS explicitly states that, outside of a CAS index, a name should be used in its uninverted form. In contrast, IUPAC nomenclature presents a name written in a continuous and linear fashion from left to right, and which contains prefixes and suffixes in a specific, linear order. The consequence is that IUPAC names for derivatives of a given parent compound would appear at different places in an index using IUPAC names because the initial letters of the names depend upon the specific prefixes employed. Two examples follow:

IUPAC, 2-sulfanylethanol CAS, 2-mercaptoethanol CAS inverted, ethanol, 2-mercapto-

In a similar sequence, we have: 4-(methylsulfanyl)benzoic acid, 4-(methylthio)benzoic acid, and benzoic acid, 4-(methylthio)-

In addition to these nomenclatures, others are current in the literature. IUBMB categorizes and specifies and names of enzymes according to the types of reaction they catalyze. Considerations of enzyme chemical structure are secondary here. The World Health Organization produces a list of nonproprietary names for drugs which are shaped so as to allow easy conversion to languages other than English and which indicate the action of the drug. Hence, the names of beta-blockers all carry the ending -olol. An example is propranolol, the structure of which is hardly reminiscent of that of propane, though the name was apparently suggested in part by the propane residues it may be considered to contain.

The International Organization for Standardization lists names for pesticides, which bear a fleeting similarity to IUPAC names; for example, "trimesium" stands for "trimethylammonium." There is also list of recommended names for cosmetic ingredients, the International Nomenclature of Cosmetic Ingredients. What characterizes these latter names is that they serve as specific identifiers for commercial and industrial materials which must be quickly recognizable by users who are nonchemists, but they are usually inadequate for use by chemists. All these non-IUPAC nomenclatures are briefly described in the new edition of Principles, together with references allowing the reader to obtain more detailed information should it be required.

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.

www.iupac.org/web/ins/2006-029-1-800


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