Step back

Those of you who were reading my blog this year might have noticed that words such as “prefix”, “suffix” or “ending” are used extensively in chemical nomenclature. And those of my readers who remember (from their school days perhaps) the basics of morphology also might have been wondering whether these terms have anything to do with their counterparts in linguistics. That’s what happens when you use terms without defining them first.

Before moving any further with nomenclature, it could be helpful to clarify our terminology.

Alas, it looks like the task is more complex than I thought. Looking through many nomenclature pages and guides, I became aware of two related but distinct problems:

• compatibility of natural language morphology with that of “chemical language”
• intercompatibility of “chemical language” morphology

The former boils down to the question whether chemical names (a) form part of a natural language or (b) belong to a special “chemical language”. In my opinion, the correct answer is (a). For example, translations of the English phrase “ethyl alcohol” to different languages behave as phrases of those languages: этиловый спирт as a part of Russian, alcohol etílico as a part of Spanish, Äthylalkohol as a part of German. Every natural language has a number of specialised subsets or vocabularies; “chemical language” is one of these vocabularies. Therefore we can expect that, say, English chemical words have the same parts as other English words.

But let’s suppose the answer is (b). In this case, we are free to define, say, “suffix” of a chemical term in a way that is completely different from “suffix” in a natural-language word. Even so, the use of “suffix” within the domain of chemical nomenclature has to be consistent: we shouldn’t call the same thing “suffix” here and “ending” there. And this is exactly what is happening with, for instance, ‘yl’ or ‘ene’.

Wouldn’t it be even better, however, in this scenario not to use the terminology already established for natural languages at all but develop chemistry-specific morphological terms instead? According to Red Book [1], chemical names are constructed from

element name roots,
multiplicative prefixes,
prefixes indicating atoms or groups — either substituents or ligands,
suffixes indicating charge,
names and endings denoting parent compounds,
suffixes indicating characteristic substituent groups,
infixes,
locants,
descriptors (structural, geometric, spatial, etc.),
punctuation.

Thus, “locants” and “descriptors”, being specific for chemical names, are neither “prefixes”, “suffixes” nor “endings”. Why don’t we call “suffixes indicating charge” something else, say “charge descriptors”, and stop confusing ourselves and others?

Nevertheless, I am going to stick to (a) for a while, that is, to treat chemical names as parts of natural language. I’d like to start with a few rather uncontroversial statements.

1. Every word contains one or more morphemes.
2. Chemical names consist of content words.
3. More specifically, chemical names are noun phrases consisting of at least one noun. Binary names include adjectives or other nouns, e.g.
   ethanol (noun)
   2-(1H-imidazol-4-yl)ethanamine (noun)
   benzoic anhydride (adjective + noun)
   hypobromous acid (adjective + noun)
   mandelonitrile β-D-glucopyranoside (noun + noun)
   copper sulfate pentahydrate (noun + noun + noun)
4. Every content word contains at least one root morpheme.
5. In addition, any content word that is a (part of a) chemical name can contain one or more affixes: prefixes, infixes, suffixes or endings.

So far so good, right? No objections? We are dealing with English chemical nomenclature but these statements should hold for other Indo-European languages too.

Now have a look at the example. For unbranched alkanes,

higher members of the series are named systematically by combining the ending -ane, characteristic of the first four members and implying complete saturation, with a multiplicative prefix of the series penta-, hexa-, etc. <...> which indicates the number of carbon atoms constituting the chain [2].

In other words, the name “pentane” consists of the prefix ‘pent(a)’ and the ending ‘ane’, with no root. Wait. That can’t be right because of (iv) above.

In another example,

The H-W <Hantzsch-Widman> system combines the ‘a’ prefixes <...> with endings, in the H-W system called stems, that indicate the size and saturation of the ring [3].

Here, the name “dioxane” consists of the prefix ‘diox’ and the ending ‘ane’ (which, by the by, is different ‘ane’ from that of “pentane”), with no root again. The word “stem” (sometimes used in linguistics as a synonym of “root”) for ‘ane’ makes much more sense. But can we really call ‘diox’ a prefix?

Watch this space.

References

1. Connelly, N.G., Hartshorn R.M., Damhus, T. and Hutton, A.T. Nomenclature of Inorganic Chemistry: IUPAC Recommendations 2005. Royal Society of Chemistry, Cambridge, 2005, p. 5.
2. Leigh, G.J., Favre, H.A. and Metanomski, W.V. Principles of Chemical Nomenclature: A Guide to IUPAC Recommendations. Blackwell Science, 1998, p. 71.
3. Hellwich, K.-H., Hartshorn, R.M., Yerin, A., Damhus, T. and Hutton, A.T. (2020) Brief guide to the nomenclature of organic chemistry (IUPAC technical report). Pure and Applied Chemistry 92, 527—539.