notes on nomenclature #-%
Nomenclature of Tautomeric Substances Even the eoal of relatine names to structures is not without its difficulties. If the goal >chemical nomenclature is to relate a name to the structure of a compound, what is to he done about tautomeric compounds which are equilibrium mixtures of two or more definite structures? Consider the keto-enol tautomerism 0 0 OH 0
II II
Kent Slate University Kent. Ohio 44242
KURT LOENING ROY M. ADAMS
Chemical Abstracts Service Columbus. Ohio 43210 Geneva College Beaver Falls. Pennsylvania 15010
CH,CCHCOC"HS . . .. ethyl 3-oxobutanoate
=
I
1I
CH,C=CHCOC,H.. " ethyl 3-hydroxy-2-hutenoate
As lone as one wishes to refer to one of the s~ecificforms. the applicable one of the above two names is siitahle. to use only one of the names for the equilibrium mixture is not completely descriptive. Yet this is what is usually done. In indexes, of course, cross-references should he given in such cases. A simple nomenclature to indicate the presence of hydrogen bonding in such a compound would be helpful
ow ever,
Chemical Nomenclature versus that of Other Sciences ( 1 )
I \./I I
HF-C-CHC-0C2Hs For words, like Nature, half reveal and half conceal the soul within. Tennyson
Chemists don't always seem to realize what a valuable asset they have in their schemes of systematic nomenclature. Let us look at the names used in mineralogy and biology. We have before us two beautiful minerals, one lavender, the other yellow. Both are known by the name lepidolite. Sometimes we ;emember the name; too often we forget it because nothing in the name tells us that it is a lithium mica or that micas are silicates containing alkali metals and aluminum. You might remember that Delonix regia is the scientific name for the flamboyant, a particularly beautiful flowering tree of the semitropics. Do you recognize Anosia plexippus as the Monarch butterfly? These names are useful because each is characteristic of an individual species by international agreement and, in the case of biological names, indicates the genus as well as the species. The names may call attention to some characteristic of the species such as color, form, etc., or to the one who first recognized the species or to the region where it was first found. However, the names do little to relate the genus or species to orders or families, or to identify the individual sufficiently to permit its recognition by a person on first sight. In chemistry the systematic name 3,6-dioxohexanoic acid enables a chemist to visualize the structure of the compound and to write OHCCH2CHzCOCH2COOHas a representation of that structure. Furthermore, with very little experience nonchemists can perform the same feat. Admittedly, 6 , l l dihvdro-6.11-e~idioxvhenzlblacridine mav seem a hit lone . . (an2 of course many chemi'cai names are much longer) but, if the name is eiven once in anv written resenta at ion, the substance can b l called A or compound I o; even Jenny from then on, if one wishes to be brief. Chemists may use codes to develop names but they usually share the key with all who wish to know it. This is not the case with those who advance boldly into thpir preientations assuming that the reader is already familisrwith theahhreviations, codes, or trivial names which-are well understood only in limited circles. 726 / Journal of Chemical Education
Chemical Abstracts Service is able to avoid a large - .art of the difficulty by assigning the same registry number to both names. Hence. in CAS information retrieval one is guided to all of the literature, regardless of which name was used in the original work. Fluxional molecules (2-4) and resonance forms lead to much greater nomenclature problems. As yet these have not been solved completely. Literature Cited i l l For a mmoarison of chemical nomenclaturewith that of other sciences see Dermer. 0. C., Gorin, and Lwning, K.: Inl. J. Socialogy Longuoge, in presn. 121 Doering, W. von E., and Roih, W. R..Angeu. Chem. Int. Ed. E n g i . 2.115 (1963) (3) Muetterfies, E. L., lnvrp. Chem.. 4,769 (19661. (1) Cotton,F.A.,Accounfs Chem Rar., 1.257 (1966).
Some U.S. Nomenclature Practices at Variance with Those Recommended by IUPAC American chemists, while subscrihine to almost all of the ILI'AC nom~nclaturepractices, consktently follow some difrerences. The names used for elements 13 and 55 are aluminum and cesium instead of aluminium and coesium rl J. Thr spelling aluminum goes hack toan action of the Council of the American Chemical Societ\.on SAnril 1926 ( 2 )IQ follow the almost universal popular usage in the United States. As sunnorted bv American dictionaries such as Wehster. it is now standard ~ k e r i c a npractice to contract the diphthongs in s words derived from the Latin or Greek. Some e x a m ~ l eare: estrone rather than oestrone, cesarian rather than caesarian, ~ h a r m a c o ~ erather ia than ~harmacoooeia.and stoichiometw ;ather than stoicheiometr;. While ~ m e r i c a nchemists have acce~tedthe name niobium for element 41,metallurgists feel strongly that the name should he columbium ( 3 4 7 . While English- and French-speaking chemists prefer tungsten, those speaking Teutonic languages prefer wolfram because in translation tungsten means heavy stone, certainly not a rhamcteristic dF5tinctive for element 74. The IUPAC Commission on the Nomenclature of Inorganic Chemistry recommends niccolate instead of nickelate. This
recommendation has found little favor among Englishspeaking chemists. Also the Commission consistently uses sodium hydrogencarbonate (NaHC03), lithium dihydrogenphosphate (LiHzPOd, etc. for the acid salts and hydrogensulfide (HS-), hydrogenphosphonate (HPHOa-), etc. for the anions. American chemists prefer to write hydrogeqin these names as a separate word: hydrogen carbonate (5-6). The IUPAC Commission on the Nomenclature of Oreanic Chemistry favors the separate words rather than the "f;sed" names (7). So also does the Chemical Societv (London) (8). noth he; difference of this same type is ox; acids. I~&AC recommendations comhine the two words whereas U S . practice is to keep them separated. Literature Cited 111 J. Amer C h ~ m Sor.. 82,5525 (19601. 121 Proc Am. Chem. S o r . 33 119261. 131 Smtt. J. D.. Chem. En& News., 37.48 (July 13,1959). 141 J. M d a l s . 325 1Mey 19581. 151 J. A m e i Chrm. Sol.. 82.5530.5536 119571. 161 Cr8ne.E. J . , J CHEM. EDUC..8.1336 119311. 171 "Nomenclature sf Owanic Chemistry, Sections A, B,and V, (3rd. Ed.1The Buttenvorth Gmup, London. 1971. Rule 462.1. 161 "Handbook ic,r Chemical Society Authors". 1961, pp. 26.34.
1) The descriptors cis (an this side) and trans (across) are still satisfactorywhere unambiguous. 2) The extension of cis and trans propxed hy Epstein and Raasini (2) greatly clarified the use of cis and tmm. 3) The "&-like" topographical nature of the letter E and the "trans-like" topographical nature of the letter Z are confusing. 4 ) Cis and trans are still retained for designating stereoisomers in monocyclic compounds, in fused ring systems with saturated bridgeheads, and in long chains in special cases (3).
The extension of cis and trans mentioned in 2) above was to specify whether the carbons of the fundamental chain adjacent to the double bond carbons are cis or trans, and to place the descriptor immediately before the number locating the double bond
However, the cisltrans system has limitations. Since suhstituents are cited in alphabetical order, separation of names of substitutents to be related stereochemically may result
Isomerism About A Double Bond: Use of CIS and TRANS A recent Note was devoted to the designation of isomerism about a double bond by the use of the descriptors Z (zusammen, together) and E (entgegen, opposed) ( I ) . James L. Lyle (California State College, Dominquez Hills, California 90747) has written urging that both the cisltrans and the ZIE systems for naming geometrical isomers he taught to undergraduate students and that the older cis-trans method has much to commend it. The specific points he makes are these:
This situation causes no problems for the E I Z system, in which the above structure would he labeled E. Literature Cited
Volume 53. Number 11, November 1976
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