35 No. 1
||A column about the Principles of Chemical Nomenclature—A Guide to IUPAC Recommendations, 2011 Edition
Someone attempting to construct a name using a specified kind of nomenclature, such as IUPAC nomenclature, or trying to discern the chemical structure implied by a name encountered in, say, an article, must first decide what kind of nomenclature is being used. Few chemists would have problems understanding a name such as sodium chloride. This is a venerable name, and the implications of the presence of the positive and negative entities of a salt are generally well understood. However, as we have seen in previous Notes, IUPAC promulgates several classes of nomenclature, sometimes specific to particular classes of compound, so that the chemist has first to decide which particular class of nomenclature should be used, or, if trying to decipher a name, which particular class has been used to construct the name under consideration.
The new edition of Principles, like the first edition, contains enormous amounts of information on how to construct names once the compound class has been recognized. This includes various classes of compound, such as organic, inorganic, organometallic, polymeric, and biochemical. However, a novel departure in the new edition is the incorporation of a new Chapter on deciphering (or deconstructing) names.
Upon encountering a new name, the chemist must first decide to which class of compound the name belongs. This is generally, but not always, straightforward. Then, for an organic compound, for example, it is recommended to decide first whether functional class or substitutive nomenclature is being used. Then, the chemist must deduce the identity of the parent hydride and hence its numbering scheme, recognize any suffixes to parent the name (there may not be any), and finally recognize the detachable prefixes and endings. These operations should enable the chemist to begin to write a structural formula. The names of biological compounds, mainly organic compounds, generally fall outside the scope of Principles, but information on the important groups of such compounds, such as sugars and nucleotides is given, and sources of more information are noted. Often the complete systematic names of such compounds may be so complicated and large that regular use requires alternative simpler, more compact names.
To name inorganic compounds, again the class of compound must be determined. A compound may span more than one class (e.g., it may be a salt and also contain a coordination entity) so that more than one system of nomenclature may need to be employed. To decipher the name of a coordination entity, the following steps are necessary: identify the central atom(s), identify the ligands (which may be organic compounds and be named using organic methods), and identify the coordination geometry and stereochemistry. The names of organometallic compounds reveal some specific aspects that need to be appreciated, and boron compounds often bear names that are derived using a different set of conventions.
The rules for constructing the names of polymeric compounds are different yet again. In decipherment, they are often easier to recognize because they contain the term “poly” at or near the beginning of the name. Then, the specific rules of the types of polymer nomenclature should be consulted to unravel the structure.
Constructing and deciphering chemical names are certainly not easy problems for a beginner, and are sometimes not easy even for the nomenclature expert. However, Principles provides a summary of methods employed in both name construction and name decipherment, replete with many examples of both kinds of process. Although the tasks of applying nomenclature rules may appear imposing, chemists should persist. A couple of old English sayings should always be remembered. One is that “practice makes perfect,” even though the most experienced nomenclaturists are still striving for perfection. None of us is ever likely to reach the stage where “familiarity breeds contempt.”
last modified 8 January 2013.
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