Editing Tip: Chemical Prefixes

Chemistry is a complicated science, and the complexity of its terminology can be seen in the names of compounds. As a follow-up to a our article about writing chemistry papers, this post focuses on prefixes commonly used with chemical compounds. Much of this information can also be found in the American Chemical Society (ACS) Style Guide, which is a very useful resource for chemists.

Here are some general rules for chemical compound prefixes. In most cases, the following descriptors are set off by hyphens and appear at the beginning or middle of a chemical name. At times, as described below, commas are used to separate items. No spaces should ever be placed between hyphens or commas.

1. Numerals

Numerals can be used to describe the position of a functional group. They are not italicized but are set off with hyphens and/or commas if more than one is needed. (e.g., 6-aminobenzothiazole or 1,2-polybutadiene).

2. Element symbols

Chemical element symbols denote attachment to a particular atom. These prefixes are italicized and hyphenated, and commas can be used (e.g., S-methylbenzenethiosulfonate, N,N'-dimethylurea, or 1H-1,3-diazepine). Note that chemical element symbols are NOT italicized when describing a specific type of reaction (e.g., O-substitution or O-substituted).

3. Greek letters

Letters from the Greek alphabet are used to denote position or stereochemistry. These should be written as letter symbols, not spelled out. They are used with hyphens and commas, when necessary (e.g., **α-hydroxy-β-aminobutyric acid**). A comma is not used when a numeral precedes a Greek letter.

4. Structural prefixes

Other descriptive prefixes can be used to denote position, stereochemistry, and configuration. These prefixes are always italicized and hyphenated, but some are capitalized and others are not. The following table shows several common prefixes, including whether they are capitalized:

5. D and L

These two prefixes indicate absolute configuration for amino acids and carbohydrates. They are written in small capital letters.

6. Plus and minus signs

Plus and minus signs can be used as stereochemical descriptors. They are always enclosed in parentheses and hyphenated (e.g., (+)-dihydrocinchonine).

We hope that this serves as a handy reference when writing your next chemistry paper! If you have a question about your writing, send us an email. Best wishes from AJE!

Special thanks to Anna Sharman for pointing out the use of small caps for L- and D-.