Capitalization of Chemical Compounds

  • Capitalization rules for chemical compounds and abbreviations can be confusing.
  • At the beginning of a sentence, capitalize the first syllabic portion of the compound name.
  • Chemical elements and amino acids are not capitalized within a sentence, just their symbol (e.g., Ag or Gln).

A separate article here on the Author Resource Center discusses formatting with chemical compound prefixes. This post focuses on capitalization of chemical compounds and abbreviations, another tricky aspect of formatting chemistry papers. Here are several tips to follow:

1. Chemical names

The names of chemicals are not capitalized unless they are the first word of a sentence. In such a case, the first letter of the syllabic portion is capitalized, not the descriptor or prefix. Note that prefixes such as Tris- and Bis- (which are not commonly italicized) are considered part of the name. The following table shows several examples.

Within sentenceBeginning a sentenceWithin sentenceBeginning a sentence
benzoic acidBenzoic acid1-bromo-3-chloropropane1-Bromo-3-chloropropane
7-(4-chlorophenyl)-1-naphthol7-(4-Chlorophenyl)-1-naphtholO,S,S-triethyl phosphorodithioateO,S,S-Triethyl phosphorodithioate
O,S,S-triethyl phosphorodithioateO,S,S-Triethyl phosphorodithioatep-benezenediacetic acidp-Benezenediacetic acid
tris(β-chloroethyl)amineTris(β-chloroethyl)aminecis-1,2-dichloroethenecis-1,2-Dichloroethene

2. Chemical elements

Within a sentence, the names of chemical elements are not capitalized, but the first letter of a chemical symbol should always be capitalized (e.g., “The sample contained calcium atoms” and “The sample contained Ca atoms”).

3. Chemical formulas

Within a sentence, the names of chemical compounds are not capitalized, but the first letter of each elemental symbol should be capitalized (e.g., “We added sodium hydroxide” and “We added NaOH). Note that symbols and words should not be mixed (that is, avoid saying “K chloride”).

4. Amino acids

Abbreviations for amino acids (three-letter or one-letter versions) are capitalized; full names are not capitalized unless they are the first word of a sentence (e.g., ““The mutant protein features a substituted glutamine residue” and “The mutant protein features a substituted Gln residue”).

We hope that today’s post provides some additional useful advice for writing or editing your next chemistry paper! Send us an email with any questions.

Share with your colleagues

Related Articles

Chemistry Writing Tips

Editing Tip: Indefinite Article Use with Elements

How to choose the right article (a or an) with chemical elements. Read More »

Chemistry Writing Tips

More Tricky Chemistry Writing Conventions

Some unique conventions found in chemistry articles you should know about. Read More »

Chemistry Writing Tips

Editing Tip: Chemical Prefixes

A guide to prefixes for chemical compounds, including hyphenation, commas, capitalization, and more. Read More »

Stay up to date

Sign up for early access to AJE Scholar articles, discounts on AJE services, and more