Wikipedia:Naming conventions (chemistry)

General rule[edit]

From Wikipedia:Naming conventions:

Generally, article naming should give priority to what the majority of English speakers would most easily recognize, with a reasonable minimum of ambiguity, while at the same time making linking to those articles easy and second nature.

IUPAC preferred name vs. systematic name[edit]

IUPAC recommends[1] the use of non-systematic names for some organic compounds, and these recommendations should be followed in article titles. Examples:

acetic acid not ethanoic acid
toluene not methylbenzene
lysine not 2,6-diaminohexanoic acid

Element names[edit]

Traditionally, the names of three elements have been spelled differently in different parts of the English speaking world. For articles about chemistry-related topics, Wikipedia follows the spellings recommended by the International Union of Pure and Applied Chemistry (IUPAC):[1][2]

aluminium not aluminum
sulfur not sulphur
caesium not cesium

These spellings should be used in all chemistry-related articles on English Wikipedia, even if they conflict with the other national spelling varieties used in the article.

This convention should also be applied to all compounds and derivative names of these chemicals: sulfate not sulphate; sulfuric not sulphuric; etc.

Capitalization of elements and compounds[edit]

In former versions of the IUPAC recommendations, names were written with a capital initial letter. This practice has been abandoned in later publications.[3] The names of chemical compounds and chemical elements when written out, are common nouns in English, rather than proper nouns. They are capitalized at the beginning of a sentence or title, but not elsewhere. Note that for chemical elements this applies to the word only and not the chemical symbol, which is always capitalized. Both rules remain even with chemical elements derived from proper names which would otherwise be capitalized, in keeping with IUPAC policy to differentiate proper names from things named after proper names. Thus, it is californium but the symbol is Cf, and einsteinium, but symbol Es. Note that names for odd or rare chemicals are uncapitalized like common ones, and thus uranium and plutonium (symbols U and Pu) should be uncapitalized like carbon or iron (symbols C and Fe). This rule (full name uncapitalized but symbol capitalized) applies also to isotopes and nuclides, when completely written out: thus 14C but carbon-14. (The element mercury is uncapitalized, but of course the planet and god Mercury remain capitalized proper nouns).

Likewise, the names of chemical compounds are considered common nouns which are capitalized at the beginning of a sentence or title, but not elsewhere. Prefixes such as sec-, tert-, ortho-, meta-, para-, alpha-, beta-, D-, L-, (+)-, (−)-, (R)-, (S)- and the numerical prefixes are not considered part of the name: the first letter of the main part of the name should still be capitalized where appropriate. Exceptions are cyclo, iso, neo, and spiro which are considered part of the name and therefore not italicized or hyphenated. Substituent groups do form part of the name: hence we use 2-Aminoethanol at the start of a sentence and 2-aminoethanol if not at the start of a sentence. Note that in this case the two wikilinks refer to separate redirects to the actual article. The article title itself is capitalized.

Prefixes in titles[edit]

When the chosen article title starts with a prefix including positional identifiers (ortho-, meta-, para-, N-, O-, α-, β-, γ-, etc.), isomeric identifiers (sec-, tert-, etc.), stereochemical identifiers (cis-, trans-, (E)-, (Z)-, etc.), chiral identifiers ((R)-, (S)-, D-, L-, (+)-, (−)-, etc.), or numbers, the first letter after the prefix in the name should be capitalized: hence titlecase 1,1,1-Trichloroethane not 1,1,1-trichloroethane. A redirect from the uncapitalized version should be created to simplify linking from other articles.

Non-numerical prefixes are italicized and uncapitalized in titles (tert-Butyl alcohol, for example). Both numerical and non-numerical prefixes are followed by a hyphen. The template {{DISPLAYTITLE}} is used to display titles which start with lowercase letters or include italics.

Note that cyclo, iso, neo, and spiro are considered part of a chemical name (such as isopropanol) and not considered prefixes. No hyphens or italics are used in these cases.

Use of Stock nomenclature[edit]

Stock nomenclature for inorganic compounds is based on the indication of the oxidation number (as a roman numeral, in parentheses) of each of the major elements in the compound, e.g. iron(III) chloride. It is widely, if sometimes incorrectly, used on Wikipedia for the titles of articles about inorganic compounds. It is not obligatory, as there are other acceptable methods for naming these compounds, but it is often preferred as the most common non-ambiguous name for a substance. The following guidelines are based on current WikiBestPractice:

  1. Only the cationic element (i.e. the element whose name appears unchanged in the compound name) is assigned its oxidation number. Except in rare cases (none at present), we do not assign the oxidation number in the anion: hence potassium permanganate not potassium manganate(VII), sodium hypochlorite not sodium chlorate(I).
  2. There is no space between the end of the element name and the opening parenthesis: hence silver(I) fluoride not silver (I) fluoride. Note that this is an exception to the usual English style for parentheses.
  3. It is not necessary to specify the oxidation number when there is no possibility of ambiguity in the compound title: hence sodium chloride not sodium(I) chloride.
  4. Stock nomenclature should only be used for ionic compounds. Compounds with a substantial degree of covalency should be named by stoichiometric nomenclature: hence titanium tetrachloride not titanium(IV) chloride.
  5. Stock nomenclature should not be used for compounds with mixed or non-integral oxidation numbers: hence triiron tetraoxide not iron(II,III) oxide (in fact, this article is difficult to name and, as an exception, redirects to magnetite).

Isotope labelling[edit]

Isotopes when written out are common nouns, and should begin with the uncapitalized element name, followed by a hyphen (not an em dash or en dash) and then the mass number. Examples are carbon-14 and uranium-235. The uncapitalized name of elements when written out (but not in symbol form) follows IUPAC convention for chemical elements, and is not changed when the isotope is written out. See N.G. Connelly, T. Damhus, R.M. Hartshorn, A.T. Hutton (eds) (2005). Nomenclature of Inorganic Chemistry (PDF). RSCIUPAC. ISBN 0-85404-438-8.CS1 maint: multiple names: authors list (link) CS1 maint: extra text: authors list (link)

For chemical reactions concerning specific isotopes, identify the isotope by its mass number (A). For example, 14C or 18F. You may use a nuclide template. Deuterium and tritium may be labelled "D", "2D", or "2H" and so on. Deuterated solvents for NMR use are customarily described variously as: CD3OD, methanol-d4; CD3SOCD3, DMSO-d6. These established systems are all acceptable, but should remain consistent within an article.

Drug-related articles[edit]

Where a compound has a WHO international nonproprietary name (INN), this should be used as the article title. Exceptions would be where the pharmaceutical use of a certain compound is secondary to other applications (commodity chemical, synthetic intermediate, etc., agriculture or industry).


From Wikipedia:Deletion policy: "Don't worry, redirects are cheap."

Redirects should be created for:

  • Alternative names for the compound, including acronyms where appropriate;
  • Alternative capitalizations, where there is a numerical prefix in the article title;
  • Formulas of simple compounds; for example H2Owater.


Even with the best will in the world, no set of guidelines can cover every case. Some articles on Wikipedia have non-standard titles through consensus that this is the most commonly used name (in scientific circumstances) for the compound concerned, whatever IUPAC or the other rules suggest. For example:

ethylene oxide not oxirane
phosphine not phosphane (and for substituted phosphines, arsine, stibine, and bismuthine)
Wilkinson's catalyst not chlorotris(triphenylphosphane)rhodium
Vaska's complex not carbonylchlorobis(triphenylphosphane)iridium
titin not methionylthreonylthreonylglutaminylalanyl...isoleucine[4]

Please do not get into revert wars over the naming of an article: the best place for discussion is on the article's talk page or (failing that) at Wikipedia talk:WikiProject Chemicals.

Groups of compounds[edit]

Organic functional groups and related compound classes[edit]

For articles about functional groups, the singular class name from the IUPAC "Glossary of Class Names"[5] is usually used, e.g. carboxylic acid, acyl chloride, alkane. Where the group is not considered to be functional, e.g. phenyl, trimethylsilyl, or is important for some other reason, e.g. trifluoromethylsulfonyl, the normal IUPAC name (under general nomenclature) for the group is used as the article title, without adding the word "group".

Organometallic compounds[edit]

The general article about the organometallic chemistry of an element should be entitled "Organo___ chemistry", for example, organolithium chemistry, organozinc chemistry. The IUPAC definition of an "organometallic compound" includes boron, silicon, arsenic, and selenium, so this title guideline also applies to organoboron chemistry, etc.[6] Depending on the metallic element, it may well be appropriate to have additional articles covering specific compounds or groups of compounds, or specific reactions.

See also[edit]


  1. ^ a b Panico R, Powell WH, Richer JC, eds. (1993). A Guide to IUPAC Nomenclature of Organic Compounds. IUPAC/Blackwell Science. ISBN 0-632-03488-2.
  2. ^ International Union of Pure and Applied Chemistry (2005). Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005). Cambridge (UK): RSCIUPAC. ISBN 0-85404-438-8. pp. 47, 248. Electronic version.
  3. ^ Preferred IUPAC Names Provisional Recommendation, September 2004; Chapter 1, par. 16 Name writing, p.80-90
  4. ^ See Longest word in English for more information.
  5. ^ Moss, G.P.; Smith, P.A.S.; Tavernier, D. (1995). "Glossary of Class Names for Organic Compounds and Reactive Intermediates Based on Structure (IUPAC Recommendations 1995)" (PDF). Pure and Applied Chemistry. 67 (8–9): 1307–1375. doi:10.1351/pac199567081307.
  6. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "organometallic compounds". doi:10.1351/goldbook.O04328
General references

External links[edit]