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).

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Lynne Hyman, PhD

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PhD, ChemistryDuke University

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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 sentence Beginning a sentence Within sentence Beginning a sentence
benzoic acid Benzoic acid 1-bromo-3-chloropropane 1-Bromo-3-chloropropane
7-(4-chlorophenyl)-1-naphthol 7-(4-Chlorophenyl)-1-naphthol O,S,S-triethyl phosphorodithioate O,S,S-Triethyl phosphorodithioate
O,S,S-triethyl phosphorodithioate O,S,S-Triethyl phosphorodithioate p-benezenediacetic acid p-Benezenediacetic acid
tris(β-chloroethyl)amine Tris(β-chloroethyl)amine cis-1,2-dichloroethene cis-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”).

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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.