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Casing of Chemical Compounds 1: Rules for Lowercase Prefixes

If there is one convention related to written English that is always observed, it is to capitalise the first word of a sentence. However, in writing or editing scientific or technical texts, this simple casing rule can get a bit complicated, especially when it comes to the names of chemical compounds. The names of some chemical compounds are always capitalised, even if they occur in the middle of a sentence. On the other hand, some other chemicals are always written in lowercase, even if they begin a sentence.

In this two-article series, we offer some tips on dealing with these various instances along with examples.

  • In Part 1, we look at rules for lowercase prefixes.
  • In Part 2, we look at rules for capitals and small capitals.

Be sure – by using a guide

Note that although this series sets out the conventions that govern the casing of chemical names and offers some working examples, it is always best to look up specific names in appropriate guides while you are writing. A good and comprehensive source to refer to is the International Union of Pure and Applied Chemistry (IUPAC).

Note about examples

In the examples provided in these articles, note that:

  • Boldface is added for emphasis.
  • An ellipsis within square brackets […] indicates the remaining text.
  • Greek letters α (alpha) and β (beta) are used where required.

Rules for lowercase prefixes

As you may know, the names of some chemicals begin with locants, in which the prefixes indicate the position or structure of an atom or of a group within a molecule. Also, locants are sometimes expressed through Greek letters or Latin/Roman (normal) letters. Notably though, the prefixes are always written in lowercase, whether they appear at the beginning of a sentence or in the middle. What you need to know is whether to use the upper case or the lower case for the letter that comes next.

a. Rules for lowercase prefixes: Greek letters

At the beginning of a sentence, the Greek prefixes are written in lowercase while the next letter is capitalised.

So, to give two examples, you should write: 

β-Endorphin […]

α-Hydroxy-β-aminobutyric acid […]

In the middle of a sentence, the Greek letters used as locants retain their lowercase and the next letter changes to lowercase.

In the two examples above, you should write: 

[…] β-endorphin […]

[…] α-hydroxy-β-aminobutyric acid […]

b. Rules for lowercase prefixes: Latin/Roman letters

Latin/Roman (normal) letters follow similar rules, except that they are written in italics.

Thus, at the beginning of a sentence, Latin/Roman locants are written in lowercase and the following letter is capitalised.

So, you should write (to give two examples):

n-Butyl iodide […]

p-tert-Butylphenol […]

So, as we discussed in the case of Greek letters, in the middle of a sentence, Latin/Roman (normal) locants retain their lowercase.

Thus, you should write (to give the same two examples):

[…] n-butyl iodide […]

[…] p-tert-butylphenol […]

c. Rules for lowercase prefixes: Stereochemicals

The convention also applies to stereochemical descriptors. 

Thus, at the beginning of a sentence, the descriptor is written in italics and lowercase. So, to give two examples, you write:

d-Camphor […]

meso-Tartaric acid […]

Continuing with the same logic that we encountered in the previous cases, in the middle of a sentence, the descriptor remains lowercase and the following letter is also given in lowercase. To use the same two examples, you write:

[…] d-camphor […]

[…] meso-tartaric acid […] 


Read next (second/final) in series: Casing of chemical compounds 2: Rules for capitals and small capitals


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