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A '''preferred IUPAC name''' (or '''PIN''') is the unique name assigned to a chemical substance from among the possible names generated by [[IUPAC nomenclature]]. It is intended for use in legal and regulatory situations.<ref>{{citation | title = Preferred names in the nomenclature of organic compounds | url = http://www.iupac.org/web/ins/2001-043-1-800 | publisher = International Union of Pure and Applied Chemistry | accessdate = 2009-11-22}}.</ref><ref name="DraftRecs">{{BlueBook2004|rec=12.1|pages=3–7}}.</ref>

The systems of chemical nomenclature developed by the [[International Union of Pure and Applied Chemistry]] (IUPAC) have traditionally concentrated on ensuring that chemical names are unambiguous, that is that a name can only refer to one substance. However a single substance can have more than one acceptable name, e.g. [[toluene]], which may also be correctly named as "methylbenzene" or "phenylmethane".

The introduction of preferred IUPAC names provides a set of rules for choosing between these multiple possibilities in situations where it is important to decide on a unique name: e.g. in
*patent specifications;
*customs regulations;
*environmental and occupational safety and health regulations; etc.
The wider choice of names remains available for more general contexts, so that [[tetrahydrofuran]] remains an unambiguous and acceptable name for the common organic solvant, even if the preferred IUPAC name is "oxolane".<ref>Rules P-53.2.2 and P-63.5, Draft recommendations 2004.</ref>

== PIN recommendations ==
The PIN recommendations for organic compounds were published in draft form in October 2004,<ref name="DraftRecs" /> and incorporated into the 2005 revision of ''[[Nomenclature of Inorganic Chemistry]]''.<ref>{{RedBook2005}}</ref> As of November 2009, PIN recommendations for inorganic compounds are still under development.<ref>{{citation | title = Preferred IUPAC Names (PINs) for Inorganic Compounds | url = http://www.iupac.org/web/ins/2006-038-1-800 | publisher = International Union of Pure and Applied Chemistry | accessdate = 2009-11-22}}.</ref> An "organic" compound, for the purposes of preferred IUPAC names, is defined as a compound which
# contains at least one carbon atom; and
# does not have any bonds between carbon and an element from groups 1–12.
This has one or two surprising effects, such as the preferred name "formonitrile" for [[hydrogen cyanide]].<ref>Rule P-66.5.1.2, Draft recommendations 2004.</ref>

In general, [[substitutive nomenclature]] is used for preferred IUPAC names, e.g. "ethoxyethane" instead of [[diethyl ether]], "tetrachloromethane" instead of [[carbon tetrachloride]]. [[Functional class nomenclature]] (also known as radicofunctional nomenclature) is used for [[acid anhydride]]s, [[ester]]s, [[acyl halide]]s and pseudohalides and [[salt (chemistry)|salt]]s. Other nomenclature systems are also used in particular circumstances.

The number of "retained" non-systematic names of simple organic compounds (e.g. [[formic acid]], [[acetic acid]]) has been much reduced for preferred IUPAC names, although a larger set of retained names is available for general nomenclature. The traditional names of simple monosaccharides, α-amino acids and a large number of natural products have been retained as preferred IUPAC names: in these cases the systematic names are very complicated and virtually never used.

== References ==
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[[Category:Chemical nomenclature]]

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