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IUPAC nomenclature is a system of naming chemical compounds and of describing the science of chemistry in general. It is developed and kept up to date under the auspices of the International Union of Pure and Applied Chemistry (IUPAC). The rules for naming organic and inorganic compounds are contained in two publications, known as the Blue Book and the Red Book respectively. A third publication, known as the Green Book, describes the recommendations for the use of symbols for physical quantities (in association with the IUPAP), while a fourth, the Gold Book, contains the definitions of a large number of technical terms used in chemistry. Similar compendia exist for biochemistry (in association with the IUBMB), analytical chemistry and macromolecular chemistry. These books are supplemented by shorter recommendations for specific circumstances which are published from time to time in the journal Pure and Applied Chemistry. This article treats the system of nomenclature in general, notably its aims and historical development. Separate articles treat the naming of organic compounds and inorganic compounds in more detail.
Aims of chemical nomenclature The primary function of chemical nomenclature is to ensure that the person who hears or reads a chemical name is under no ambiguity as to which chemical compound it refers: each name should refer to a single substance. It is considered less important to ensure that each substance should have a single name, although the number of acceptable names is limited. It is also preferable that the name convey some information about the structure or chemistry of a compound. CAS numbers form an extreme example of names which do not perform this function: each refers to a single compound but none contain information about the structure. One might be tempted to add 7647-14-5 to one's meal, but not 133-43-9—the former is sodium chloride, the latter sodium cyanide. The form of nomenclature which should be used depends on the public to which it is addressed: as such there is no single correct form, but rather different forms which are more or less appropriate in different circumstances. A common name will often suffice to identify a chemical compound in a particular set of circumstances. There is little risk that the "salt" on a dinner table will be sodium cyanide (technically a salt itself)! To be more generally applicable, the name should indicate at least the chemical formula: hence table salt is referred to chemically as sodium chloride, which indicates by the rules of inorganic nomenclature that the formula is NaCl. To be more specific still, the three-dimensional arrangement of the atoms may need to be specified: there are occasions where it might be necessary to distinguish between sodium chloride (halite structure) (the common form) and sodium chloride (CsCl structure) (of theoretical interest only). In a few specific circumstances (such as the construction of large indices), it becomes necessary to ensure that each compound has a unique name: this requires the addition of extra rules to the standard IUPAC system (the CAS system is the most commonly used in this context), at the expense of having names which are longer and less familiar to most readers. Other system gaining popularity is International Chemical Identifier - InChI - while InChI symbols are not human readable they contain complete information about substance structure. That makes them more general than CAS numbers. The IUPAC system is often criticized for these above failures when they become relevant (for example in differing reactivity of sulfur allotropes which IUPAC doesn't distinguish). While IUPAC has a human-readable advantage over CAS numbering, it would be difficult to claim that the IUPAC names for some larger, relevant molecules (such as rapamycin) are human-readable, and so most researchers simply use the informal names. History
Types of nomenclature See also | ||||||||||
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