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'''IUPAC nomenclature''' is a system of naming [[chemical compound]]s 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 compound|organic]] and [[inorganic compound]]s are contained in two publications, known as the ''[[Nomenclature of Organic Chemistry|Blue Book]]''<ref>{{citation | title = Nomenclature of Organic Chemistry | origyear = 1958 (A: Hydrocarbons, and B: Fundamental Heterocyclic Systems), 1965 (C: Characteristic Groups) | year =1971 | edition = 3rd  | publisher = Butterworths | location = London | isbn = 0408701447}}.</ref><ref name="bluebook">{{BlueBook1979}}. {{BlueBook1993}}. {{BlueBook2004}}.</ref> and the ''[[Nomenclature of Inorganic Chemistry|Red Book]]''<ref name="redbook">{{RedBook2005}}.</ref> respectively. A third publication, known as the ''[[Quantities, Units and Symbols in Physical Chemistry|Green Book]]'',<ref name="greenbook">{{GreenBook2nd}}. {{GreenBook3rd}}</ref> describes the recommendations for the use of [[symbol]]s for [[Physical quantity|physical quantities]] (in association with the [[IUPAP]]), while a fourth, the ''[[Compendium of Chemical Terminology|Gold Book]]'',<ref name="goldbook">{{GoldBook2nd}}.</ref> contains the definitions of a large number of technical terms used in chemistry. Similar compendia exist for [[biochemistry]]<ref name="biochem">{{WhiteBook2nd}}.</ref> (the ''White Book'', in association with the [[IUBMB]]), [[analytical chemistry]]<ref name="anal">{{OrangeBook3rd}}.</ref> (the ''[[Compendium of Analytical Nomenclature|Orange Book]]''), [[macromolecular chemistry]]<ref name="macro">{{PurpleBook}}.</ref> (the ''Purple Book'') and [[clinical chemistry]]<ref>{{SilverBook}}.</ref> (the ''Silver Book''). These "colour books" are supplemented by shorter recommendations for specific circumstances which are published from time to time in the [[Scientific journal|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 [[IUPAC nomenclature of organic chemistry|organic compounds]] and [[IUPAC nomenclature of inorganic chemistry|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 to: 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 number]]s 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. 

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. 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 nomenclature|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. Another system gaining popularity is the [[International Chemical Identifier]]&mdash;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 the 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 ==
[[File:Lavoisier nomenclature.gif|right|thumb|First page of Lavoisier's ''Chymical Nomenclature'' in English.]]

The nomenclature of [[alchemy]] is rich in description, but does not effectively meet the aims outlined above. Opinions differ whether this was deliberate on the part of the early practitioners of alchemy or whether it was a consequence of the particular (and often esoteric) theoretical framework in which they worked.

While both explanations are probably valid to some extent, it is remarkable that the first "modern" system of chemical nomenclature appeared at the same time as the distinction (by [[Antoine Lavoisier|Lavoisier]]) between [[Chemical element|elements]] and [[Chemical compound|compounds]], in the late eighteenth century.

The [[France|French]] chemist [[Louis-Bernard Guyton de Morveau]] published his recommendations<ref name="guyton">{{citation | last = Guyton de Morveau | first = L. B. | authorlink = Louis-Bernard Guyton de Morveau | year = 1782 | journal = J. Phys. | volume = 19 | pages = 310}}.</ref> in 1782, hoping that his "constant method of denomination" would "help the intelligence and relieve the memory". The system was refined in collaboration with [[Berthollet]], [[Antoine François, comte de Fourcroy|de Fourcroy]] and [[Antoine Lavoisier|Lavoisier]],<ref name="french">{{citation | last1 = Guyton de Morveau | first1 = L. B. | authorlink1 = Louis-Bernard Guyton de Morveau | last2 = Lavoisier | first2 = A. L. | authorlink2 = Antoine Lavoisier | last3 = Berthollet | first3 = C. L. | authorlink3 = Claude Louis Berthollet | last4 = Fourcroy | first4 = A. F. de | authorlink4 = Antoine François, comte de Fourcroy | year = 1787 | title = Méthode de Nomenclature Chimique | url = http://imgbase-scd-ulp.u-strasbg.fr/displayimage.php?album=692&pos=3 | location = Paris | publisher = Cuchet}}.</ref> and promoted by the latter in a textbook which would survive long after his death at the [[guillotine]] in 1794.<ref name="lavoisier">{{citation | last = Lavoisier | first = A. L. | authorlink = Antoine Lavoisier | year = 1801 | title = [[Traité Élémentaire de Chimie]] | edition = 3e | location = Paris | publisher = Deterville}}.</ref> The project was also espoused by [[Jöns Jakob Berzelius]],<ref name="berzelius">{{citation | last = Berzelius | first = J. J. | authorlink = Jöns Jakob Berzelius | year = 1811 | journal = J. Phys. | volume = 73 | pages = 248}}.</ref><ref name="berzelius-2">{{citation | title = Jöns Jacob Berzelius A Guide to the Perplexed Chemist | first = Jaime | last = Wisniak | journal = Chem. Educator | year = 2000 | volume = 5 | issue = 6 | pages = 343–50| doi =  10.1007/s00897000430a}}.</ref> who adapted the ideas for the German-speaking world.

The recommendations of Guyton covered only what would be today known as inorganic compounds. With the massive expansion of organic chemistry in the mid-nineteenth century and the greater understanding of the structure of organic compounds, the need for a less ''ad hoc'' system of nomenclature was felt just as the theoretical tools became available to make this possible. An international conference was convened in [[Geneva]] in 1892 by the national chemical societies, from which the first widely accepted proposals for standardization arose.<ref name="ref1892">{{citation | title = Congrès de nomenclature chimique, Genève 1892 | url = http://gallica.bnf.fr/ark:/12148/bpt6k2820064.image | journal = Bull. Soc. Chim. Paris, Ser. 3 | volume = 7 | pages = xiii–xxiv | year = 1892}}.</ref>

A commission was set up in 1913 by the Council of the International Association of Chemical Societies, but its work was interrupted by [[World War I]]. After the war, the task passed to the newly formed [[International Union of Pure and Applied Chemistry]], which first appointed commissions for organic, inorganic and biochemical nomenclature in 1921 and continues to do so to this day.

== Types of nomenclature ==
===Organic chemistry===
*[[Substitutive nomenclature|Substitutive name]]
*[[Functional class nomenclature|Functional class name]], also known as a radicofunctional name
*[[Conjunctive nomenclature|Conjunctive name]]
*[[Additive nomenclature|Additive name]]
*[[Subtractive nomenclature|Subtractive name]]
*[[Multiplicative nomenclature|Multiplicative name]]
*[[Fusion nomenclature|Fusion name]]
*[[Hantzsch–Widman nomenclature|Hantzsch–Widman name]]
*[[Replacement nomenclature|Replacement name]]

===Inorganic chemistry===
====Compositional nomenclature====
Examples of [[Compositional nomenclature|compositional names]] are:
* PCl<sub>5</sub> [[phosphorus pentachloride]]
* Ca<sub>2</sub>P<sub>3</sub> dicalcium triphosphide
An alternative method uses the [[oxidation state]] on the metal in place of suffices, e.g.:
* SnCl<sub>2</sub>, [[tin(II) chloride]] as an alternative to tin dichloride. 
Generally this system, known as [[Stock nomenclature]], is preferred over the prefix system for [[ionic compounds]].

====Substitutive nomenclature====
This naming method generally follows established IUPAC organic nomenclature. [[Hydrides]] of the main group elements (groups 13–17) are given -ane base names, e.g. [[borane]], BH<sub>3</sub>, [[phosphane]], PH<sub>3</sub> (the name [[phosphine]] is also in common use, but is not recommended by IUPAC). The compound PCl<sub>3</sub> would be named substitutively as trichlorophosphane. 

====Additive nomenclature====
This naming method has been developed principally for coordination compounds although it can be more widely applied. An example of its application is:
*[CoCl(NH<sub>3</sub>)<sub>5</sub>]Cl<sub>2</sub> pentaamminechloridocobalt(2+) chloride
Note that [[ligands]] such as chloride become chlorido- rather than chloro- as in substitutive naming.

== See also ==
* [[List of chemical compounds with unusual names]]

==References==
{{reflist|2}}

== External links ==

* [http://old.iupac.org/publications/books/seriestitles/nomenclature.html IUPAC Nomenclature Books Series] (list of all IUPAC nomenclature books, and means of accessing them)
* [http://www.iupac.org/publications/compendium/index.html IUPAC Compendium of Chemical Terminology] ("''Gold Book''")
* [http://old.iupac.org/publications/books/gbook/index.html Quantities, Units and Symbols in Physical Chemistry] ("''Green Book''")
* [http://www.acdlabs.com/iupac/nomenclature/ IUPAC Nomenclature of Organic Chemistry] ("''Blue Book''")
* [http://old.iupac.org/publications/books/author/connelly.html Nomenclature of Inorganic Chemistry IUPAC Recommendations 2005] ("''Red Book''")
* [http://www.chem.qmul.ac.uk/iupac/ IUPAC Recommendations on Organic & Biochemical Nomenclature, Symbols, Terminology, etc.] (includes IUBMB Recommendations for biochemistry)

[[Category:Chemical nomenclature|*IUPAC]]

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