Systematic chemical names are created, at least in part, on paper, and probably were never meant to be pronounced. It is not only about the length: locants, descriptors, punctuation marks and combinations thereof render many chemical names practically unpronounceable. Yet these names are part of language, and languages tend to change towards pronounceability. Let’s look at a few examples.
There is a class of chemical descriptors known as “geometrical and structural affixes” [1]. You might remember them being used in the names of inorganic polynuclear entities and boron hydrides. It is easy to see that most of them are not affixes but combining forms. Typically, they contain Greek or Latin roots. The descriptor cyclo is identical to ‘cyclo’ in the names of organic alicyclic compounds and cognate to the terminal ‘cycle’ in the inorganic ring nomenclature. Likewise, catena is identical to the terminal ‘catena’ in the inorganic chain names. Moreover, descriptors such as antiprismo, triangulo and hexahedro are “further analysable”, to use Laurie Bauer’s terminology [2]. The same list [1] includes several Greek letters which are pronounceable (as ‘delta’, ‘lambda’, ‘kappa’, etc.) but do not have any intrinsic semantics related to chemical structures.
The descriptors ‘cis’ and ‘trans’, however, are true prefixes. They are easily recognisable by non-chemists because they are identical to the corresponding Latin prefixes. Historically, they have been employed in geographical names, e.g. Cisjordan “on this side of the River Jordan”, Transjordan “on the other side of the River Jordan”, Transylvania “beyond the woods”, Cisplatina “on this side of the Río de la Plata”*, etc. More recently, the use of ‘cis’ and ‘trans’ in the context of gender became widespread (and widely criticised). In systematic and semi-systematic chemical names, cis and trans are italicised and followed by dashes. In trivial names, which are much more likely to be spoken, there is no need for these decorations. Remember cisplatin (a) and transplatin (b)?
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In the nomenclature of natural products like carotenoids and retinoids, the descriptor ‘all’ in conjunction with ‘cis’ and ‘trans’ indicates that all double bond configurations are identical [3]. For instance, the structure (c) can be named all-trans-retinol, which is way shorter than (2E,4E,6E,8E)-3,7-dimethyl-9-(2,6,6-trimethylcyclohex-1-en-1-yl)nona-2,4,6,8-tetraen-1-ol.
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The descriptors ‘(+)’, ‘(−)’, ‘d’, ‘l’ indicate that the compound in question as a whole has optical activity. Easy to write, awkward to say aloud. Luckily, there are alternatives ‘dextro’, ‘dex’ (from the Latin dexter, “right”) and ‘laevo’, ‘levo’, ‘lev’ (from the Latin laevus, “left”) that can be used to create rather euphonious names. They are not prefixes but content morphemes†.
As we’ve seen on the example of amphetamine, the “right” and “left” of optical rotation descriptors do not correspond to the “right” and “left” of the absolute configuration descriptors: dextroamphetamine (d) is the S-isomer and levoamphetamine (e) is the R-isomer.
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What about stereodescriptors ‘R’ and ‘S’? Curiously enough, they too found their way to trivial names of arketamine (f) and esketamine (g).
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| (f) | (g) |
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Of course, ‘ar’ and ‘es’ are nothing else than ‘R’ and ‘S’, once again stripped of their (unpronounceable) decorations. I don’t know whether we can or should consider them prefixes. Nor whether they always sound good. Try saying, for example, ‘arnorreticuline’ for (R)-norreticuline (I am making this up) or ‘eszopiclone’ for R-isomer of zopiclone (true story).
To sum up: pronounceable chemical descriptors can form parts of trivial names. Some of them end up as prefixes, some as combining forms and yet others as something else.
| * | The name of historical Cisplatina province (now Uruguay) is cognate to cisplatina, the Spanish international nonproprietary name (INN) of cisplatin. This is because the Spanish word platina “platinum” is a diminutive of plata “silver”. Cisplatina was a Brazilian province and “on the same side of <the Río de la> Plata” really means “on the same side of the Río de la Plata as Brazil”. |
| † | In English, the cognates of dexter include standalone words dexterity and dextrous. Apart from chemistry, the root laevo/levo can be found in medical terms, laevocardia, levoscoliosis and so on. |
References
- 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. 259, Table V.
- Bauer, L. (1983) English Word-Formation. Cambridge University Press, 1983, pp. 20—22.
- Favre, H.A. and Powell, W.H. Nomenclature of Organic Chemistry: IUPAC Recommendations 2013 and Preferred IUPAC Names. Royal Society of Chemistry, Cambridge, 2014, P-101.6.3.
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