A Translator’s Guide to Organic Chemical Nomenclature

Parts 1 to 19 of this series, published over the past six years, have attempted to impart a somewhat systematic but rudimentary understanding of the "rules" of organic chemical nomenclature. It's time now to put this information to work in a more translation-oriented way.

Latecomers to the series can obtain Parts 1 to 19 on a floppy disk as a ZIPped file of the .DOC and .HTM documents, for the cost of shipping. For details, contact the author at cclaff@cs.com.

Part XIX left us with the rules for naming 6-membered heterocyclic compounds containing nitrogen. Instead of systematically tabulating the names for other ring sizes and other hetero atoms, we're about to tackle the nomenclature of a few of them by a step-by-step dissection of a chemical patent.

1. Neue substituierte Thiazole und Oxazole der allgemeinen Formel

in der

A eine gegebenenfalls durch Methyl- oder Ethylgruppen mono- oder disubstituierte n-Alkylengruppe mit 2 oder 3 Kohlenstoffatomen ... [bedeutet] ,

X ein Sauerstoff- oder Schwefelatom ... [bedeutet] ...

1. Nouveaux thiazoles et oxazoles substitués de formule générale

dans laquelle

A représente un groupe n-alcoylène avec 2 ou 3 atomes de carbone, éventuellement mono- ou disubstitué par des groupes méthyle ou éthyle,

X représente un atome d'oxygène ou de soufre ...

Although this translation would be straightforward, a diligent technical translator will want to compare the text with the structural formula to verify that the source language description is correct. If not, a Translator's note is in order.

First, however, in the case of the German text it is necessary to find the verb ("bedeutet") that goes with "A". Although the verb directly follows the subject "A" in English, it is 131 words after the subject in this German claim. One reason for this immediate search is to be certain that the verb is not modified by "nicht", which would reverse the meaning of the claim. There is a certain excitement in this search, akin to that of changing a flat tire in a snowstorm.

A glance at Formula I shows that some of the bonds are not directly connected to specific ring atoms. This signifies that the bonds can be connected arbitrarily to any one of several ring atoms, giving rise to numerous possible positional isomers (cf. Part XIX).

Now, what are thiazoles and oxazoles?

Referring to the Hantzsch-Widman tables (Part XIX), we find that the suffix -ole signifies a 5-membered ring with the maximum possible number of double bonds; the prefix thia- signifies a sulfur atom in the ring; the prefix oxa- signifies an oxygen atom in the ring; and the (second) prefix aza- means there is also a nitrogen atom in the ring.

A brief digression is called for at this point to extend the discussion to the names and structures of the fully double-bonded (unsaturated) 5-membered heterocyclic compounds containing only one nitrogen, oxygen, or sulfur atom:

Hantzsch-Widman name: Trivial name:	Oxole Furan
Hantzsch-Widman name:   Trivial name:	Thiole Thiophene
Hantzsch-Widman name: Trivial name:	Azole Pyrrole

The double prefixes in thiazole and oxazole in our patent indicate 2 hetero atoms in the rings as follows:

Thiazole:
Oxazole:
1,2-Thiazole: (Isothiazole)
1,2-Oxazole: (Isoxazole)

It's clear that if X = S or O, the text of our patent correctly identifies substituted thiazoles and oxazoles.

As for the definition of A, we learned earlier that the prefix n- in n-alkylene means a straight chain of carbon atoms, and that the suffix -ylene means a group substituted at both ends. The only such unsubstituted n-alkylene groups with 2 or 3 carbon atoms are:

-CH₂CH₂- and -CH₂CH₂CH₂-.

Given the option of mono- or disubstitution with methyl (-CH₃) or ethyl (-C₂H₅) groups, a large number of other groups are possible, including:

-CH(CH₃)CH₂-,

-CH₂CH(CH₃)-,

-CH(CH₃)CH(CH₃)-,

-C(CH₃)₂CH₂-,

-CH₂C(CH₃)₂-,

-CH(C₂H₅)CH₂-,

-CH(C₂H₅)CH(CH₃)-,

-CH₂CH₂CH(C₂H₅)-,

and so on.

Armed with this analysis, we can confidently translate this part of Claim 1 as follows:

1. New substituted thiazoles and oxazoles of the general formula

in which

A denotes a n-alkylene group which is optionally monosubstituted or disubstituted by methyl or ethyl groups and has 2 or 3 carbon atoms,

X denotes an oxygen or sulfur atom, ...

The translation of "bedeutet" or "représente" as "denotes" is perfectly satisfactory, but "signifies", "stands for", or "represents" are equally acceptable.

Part XXI will continue the analysis of this patent.