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N O V . I I ,1957
NOMENCLATURE by LEONARD T. CAPELL
Thio and Thia The prefix thio is used in organic nomenclature to indicate t h e replacement of oxygen b y sulfur, as in thioacetic acid, CH 3 CSOH or CH3COSH, a n d as a connective or doubling radical a s in 3-(methylthio) propionic acid (MeSCH 2 CH 2 C 0 2 H ) or thiodiacetic acid [S(CH2C03H)2]. Thia is the approved "a"-name prefix for indicating t h e replacement of carbon and its attached hydrogen i n a hydrocarbon chain or ring. Thio should n o t b e used to indicate replacement of carbon, a n d thia should n o t b e used to indicate replacement of oxygen. Strict adherence to these concepts will lead to some changes in present names. Thus thiopyran, thiomorpholine, a n d thioxanthene would b e better, respectively, than thiapyran, thiamorpholine, a n d thiaxanthene. T h e chief advantage of t h e latter names is for grouping with other thia names in indexes. Of the trivial names thiophene, thionaphthene (thianaphthene) a n d thiophanthrene, in which neither thio nor thia can b e justified, thiophene is so common that a change should not even be considered. Benzo[b]thiophene a n d naphthoic 2,3-fr] thiophene, respectively, should b e considered seriously as replacements for t h e others. T h e use of t h i or thia i n Hantzsch-Widman names such as thiazole and thiadiazine is correct usage.
The na-me morpholine was given in 1889 to O . C H 2 . C H 2 . N H . C H 2 . C H 2 because i t was erroneously b e lieved that morphine contained t h e same ring system. T h e similarity in names has caused little concern since pnactically no morpholine compounds have been used in medicine until recently. Now, however, a new class of compounds containing the morpholine ring h a s been made available for such use. These compounds are said to have no similarity either chemically or pharmacologically t o morphine. Should w e give -the morpholine nomenclature another look?
Rings "The Ring Index" (ACS Monograph Mo. 8 4 ) , n o w out of print, has information o n over 4000 ring systems used in organic chemistry. I n the 1 6 years since its publication in L941 there have appeared in the abstracted literature approximately 3600 n e w rings. Thus t h e total number of known ring systems is now rapidly approaching 8000, if indeed it has not already exceeded tliat number. The present rate of increase is approximately 5O0 new rings a year.
Nor
The r>refix nor is n o w officially a part o f o u r nomenclature. In steroid nomenclature it indicates t h e elimination of one C H 2 group from a m e t h y l group, from a chain, o r from SL ring. I n terpene nomenclature nor means t h e complete Morpholine and Morphine stripping of methyl groups from Some pharmaceutical chemists t h e parent c o m p o u n d . Arthur E . are beginning to question the ad- Meyer writes: "Hardly any chemvisability of naming derivatives of ist knows h o w t h e prefix 'nor* tetrahydro-l,4-oxazine (commonly originated. W h e n I was . . . with called morpholine) a s substituted t h e German Bayer Company one of morpholines. Their argument i s t h e older chemists brought over a thai "while a chemist who is well bottle labeled 'norbase.' I asked versed in chemical nomenclature what that meant and was told that knows t h e structure of morpholine, t h e original base h a d a substituted a physician may think that a d r a g amino gxoup. This h a d no substitdescribed a s a morpholine conn- uent so that i t was *N ohne Radical,' pound i s a derivative of morphine/' abbrevia-ted nor."
