For compounds of biological importance, see Biochemistry.
Caution! Chemical compound names follow complex rules, and should be written and edited with great care. Some basic rules for expressing compound names are shown in this section, but writers and editors should refer to the International Union of Pure and Applied Chemistry(Opens in a new tab/window) (IUPAC) and other standards for chemistry terminology to check the accuracy of all names; see Chemistry terminology.
Chemical formulas
Chemical compounds (ie a molecule that contains atoms of more than 1 element) are represented by formulas that show the number of the different atoms in the molecule. Show the number of atoms of each element in the molecule in the right-hand subscript position:
NH4 Al2O3
In general texts, it is best to write out simple chemical compound names in full, wherever possible (e.g. carbon dioxide, methanol, sodium acetate); however, in technical reports and scientific journal papers, it might be appropriate to use the symbol (especially in tables and figures). If abbreviations for chemical symbols are used, consider identifying them in full at first use in text, and in notes under tables or figures:
sodium chloride (NaCl) sulfuric acid (H2SO4)
Use spaces between ions and neutral segments of a chemical compound when written in full, but keep chemical formulas without spaces:
sodium chloride (NaCl) magnesium potassium fluoride (MgKF)
Trivial versus systematic names
Chemical compounds can be named by their trivial (common), systematic or semisystematic names:
acetone [trivial name], propan-2-one [systematic name]
water [trivial name], hydrogen oxide [systematic name]
benzene carboxylic acid [systematic name], benzoic acid [semisystematic name]
Use IUPAC names for simple organic compounds (e.g. alcohols):
methanol not methyl alcohol
ethanol not ethyl alcohol
Capitals in chemical names
Do not use initial capitals for chemical names unless they are proprietary names or are used at the beginning of a sentence or part of a title:
Roundup but glyphosate
methyl propyl ether [in running text]
Methyl propyl ether [at the beginning of a sentence, or in a title if the style for titles is sentence case]
Methyl Propyl Ether [in a title if the style for titles is initial capitals]
See also 'Locants, descriptors and isomers' on this page.
Prefixes in chemical names
Set solid prefixes that denote multiplication or are integral parts of the name:
cyclohexane dinitrogen oxide isopentane
Locants, descriptors and isomers
Locants are numbers or letters that indicate the positions of functional groups in a molecular structure. The numbers or letters are placed immediately before the part of the name that they relate to and are set off with hyphens:
but-1-ene not 1-butene 3,5-decadien-1-yne
The prime symbol (see Single prime symbol) indicates the position of the functional groups in multi-ring compounds:
3'-methylphthalanilic acid
Letters are italicised:
(Z)-2-butene (2E,5Z)-2,5-decadiene
Also use italics for substituted chemical element symbols:
N-methylethanamine S-ethylcysteine
When element symbols are used with a type of reaction to form an adjective or noun, roman type can be used to distinguish this use from the use of element symbols as substituted atoms:
N-acetylated O-substitution
Note: Some organisations and journals do not follow this style rule.
Use italics for cis- and trans- isomer names, and all other positional, stereochemical, configurational, symmetry and descriptive prefixes, whether with the full name or an abbreviation:
9-cis-retinal trans-1,2-dichlorocyclohexane meso-3,4-dichlorohexane o-methylphenol p,p'-DDT
R (rectus/right-handed) and S (sinister/left-handed) stereocentre designations are given in italics and brackets:
(R)-2-bromobutane (S)-2,3-dihydroxypropanol
Use small capitals for D (dexter/on the right) and L (laevus/on the left) optical isomers (however, take care when using this notation as it has been largely superseded by the R, S system):
-glucose -alanine
Ignore italicised elements and locants when capitalising at the beginning of sentences or in headings:
9-cis-Retinal is … o-Methylphenol can be … N-methylethanamine was …
Chemical bonds
It is not necessary to show chemical bonds in formulas unless they are specifically required for discussion:
CH3COOH
If it is necessary to indicate bonds in running text, use unspaced en dashes:
the angle of the C–C–C bonds
How to insert an en dash:
In Windows (e.g. Microsoft Word), use Ctrl+- on the numerical keypad; use Alt+0150 on the numerical keypad; or insert from the symbol set (special characters). On a Mac, use Option+-. Word can also be set up to convert 2 hyphens (--) to an en dash (–) using the autocorrect options.
When necessary, show double and triple bonds as follows:
CH3C(=O)OH CH3C≡CH
Polymers
A polymer is a structure composed of macromolecules. For common names of polymers, the prefix poly is set in roman type, lower case, and solid with the rest of the name, which may or may not be in brackets:
polyacrylamide poly(vinyl chloride) [Poly(vinyl chloride) at the start of a sentence]
Other descriptors are given in lower case and italics (e.g. graft, blend, co, per):
poly(3-hexylthiophene)-blend-polystyrene poly(styrene-co-isoprene)
IUPAC has a good guide: A brief guide to polymer nomenclature(Opens in a new tab/window).