A chemical nomenclature is a set of rules to generate systematic names for chemical compounds. The nomenclature used most frequently worldwide is the one created and developed by the International Union of Pure and Applied Chemistry (IUPAC).
The IUPAC's 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'',〔''Compendium of Chemical Terminology, IMPACT Recommendations (2nd Ed.)'', Oxford:Blackwell Scientific Publications. (1997)〕 contains the definitions of a large number of technical terms used in chemistry. Similar compendia exist for biochemistry〔''Biochemical Nomenclature and Related Documents'', London:Portland Press, 1992.〕 (the ''White Book'', in association with the IUBMB), analytical chemistry〔.〕 (the ''Orange Book''), macromolecular chemistry〔''Compendium of Macromolecular Nomenclature'', Oxford:Blackwell Scientific Publications, 1991.〕 (the ''Purple Book'') and clinical chemistry〔.〕 (the ''Silver Book''). These "color books" are supplemented by shorter recommendations for specific circumstances that are published from time to time in the journal ''Pure and Applied Chemistry''.
== Aims of chemical nomenclature ==
The primary function of chemical nomenclature is to ensure that a spoken or written chemical name leaves no ambiguity concerning which chemical compound the name refers to: each chemical name should refer to a single substance. A less important aim is to ensure that each substance has a single name, although a limited number of alternative names is acceptable in some cases.
Preferably, the name also conveys some information about the structure or chemistry of a compound. CAS numbers form an extreme example of names that do not perform this function: each CAS number refers to a single compound but none contain information about the structure.
The form of nomenclature used depends on the audience to which it is addressed. As such, no single ''correct'' form exists, but rather there are different forms that 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. To be more generally applicable, the name should indicate at least the chemical formula. To be more specific still, the three-dimensional arrangement of the atoms may need to be specified.
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 that are longer and less familiar to most readers. Another system gaining popularity is the International Chemical Identifier (InChI)— which reflects a substance's structure and composition, making it more general than a CAS number.
The IUPAC system is often criticized for the above failures when they become relevant (for example, in differing reactivity of sulfur allotropes, which IUPAC does not 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.
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