Tautomery

B. Eistert, Tautomerie und Mesomerie. Enke, Stuttgart, Germany, 1938. 

Kwiatkowski and Lesczcynski and (2) Nowak, Adamowicz, Smets, and Maes. Within the harmonie approximation, ab initio methods yield very aeeurate frequeneies for the fundamental vibrations (normal eoor-dinate ealeulations) although in most eases the values need to be sealed (sealing faetor 0.9 to 0.98 depending on the theoretieal method used). The eomparison with the experimental speetrum suffers for the following reasons (1) most tautomerie eompounds are studied in solution while the ealeulated speetrum eorresponds to the gas phase (2) eombination, overtone, and Fermi resonanee bands are not eomputed and (3) ealeulations are mueh less aeeurate for absolute intensities than for frequeneies. This last problem ean be partially overeome by reeording the eomple-mentary Raman speetrum. Some representative publications are shown in Table V. 

Sinee the last review (76AHCS1, p. 226), mueh work has been done in the area of 2,3-dihydroxyfurans. Compounds of this type (a-keto-y-butyrolae-tones) exist in two tautomerie forms 35 and 36. 

Tautomerie equilibria of 3-acyltetronie aeids are more eomplex. Without taking a triketo tautomer and 4 isomers into eonsideration, there are four... 

As has been pointed out previously, 4-aroyl-3-hydroxy-2(5//)furanones 50 are enolie. The eorresponding imine exists as the tautomerie diearbonyl strueture 51 (93JHC161) (Sehemes III and IV of this reference eontain printing errors). For more information see also (91JHC1501). 

Despite the speeial features eharaeteristie of annular tautomerism in eaeh individual azole system, some generalization regarding the thermody-namies and kineties of these tautomerie equilibria and their dependenee on strueture and media ean be proposed. 

Dithione tautomerie form 224b was identified from IR speetroseopy [76AHC(S1), p. 459 96UK326] as predominant for 3,5-dimereapto-l,2,4-thiadiazole and its derivatives (Seheme 76). 

All four tautomerie forms have been deteeted by UV studies in aqueous solution for pyridazino[4,5-h]indole system in the relative abundanee of 10 10 lOA 1 for 57a, 57b, 57c, and 57d, respeetively (93T11145). Tire ex-istenee of 8-arylazoguanines (58) in the 9//-oxoamino form in the solid state and in solution has been proved by the detailed IR, and and NMR studies [91AP(324)133]. 

A -Acetyl derivatives 125 and 126 exist as tautomerie mixtures in DMSO-dg at room temperature (for both, A [a]/[t] = 1-5) at elevated temperature the proportion of the azido form inereased. In CDCI3, the azido form only was deteeted for 125 for 126, a 126A 126T ratio was ehanged to 10 1. 

Six-six condensed heterocyelie systems without a tautomerie funetional group(s) [for instanee, pteridine 135 (R = = R" = H)], do not exhibit pro-... 

Comparison of the UV speetra of 5-amino-2-(2-furyl)-l,2,4-triazolo[l,5-cjquinazolines (196) and its 5-methylamino derivative (197) in neutral, aeidie, and basie media with the speetra of the two tautomerieally looked derivatives—2-(2-furyl)-5-dimethylamino-l,2,4-triazolo[l,5-c]quinazolines (198) (amino-loeked tautomers) and the imino-loeked tautomers 2-(2-furyl)-5-imino-6-methyl-l,2,4-triazolo[l,5-c]quinazolines (199)—indieated that eompounds 196 and 197 are best represented as a mixture of their amino and imino tautomers (88JMC1014) (Seheme 75). 

The nonsymmetrie dimethylhydrazine adds exelusively to the triple bond of the ynaminoketones (70-75°C, THF, CH2CI2, 3 h) to form A,A-dialkylamides of 3-oxobutanohydrazonie aeid, whieh exist in solution as a tautomerie mixture of the hydrazonie (371) and enhydrazinie (372) forms, yields 49-54% (87ZOR1635). 

The introduetion of strong eleetron-donating groups into positions 4 and 6 (but not into position 2) leads to a further shift of the tautomerie equilibrium toward... 

In solution, the position of the tautomerie equilibrium of 1,2-dihydropyrimidines is highly infiueneed by the polarity of the solvent The eontent of the more polar 1,2-dihydro tautomer is greatly inereased in DMSO-iie due to strong intermoleeular bonding with the solvent eompared to that in CDCI3, as shown in Table I. 

A variety of 2H- (121, X = O) and 4H- (122, X = O) 1,3,5-oxadiazines has been studied and eharaeterized, whereas 2//-l,3,5-thiadiazines 121 (X = S), unlike the 4H isomers 122 (X = S), are uneommon. The most eommon type of tautomerie intereonversions for sueh systems is ring-ehain tautomerism. A few studies on substituent tautomerism have also been earried out however, no data on annular tautomerism have yet appeared in the literature. 

In eontrast, 1,2,6-thiadiazines, espeeially their 1,1-dioxide derivatives, are eommon. N-Unsubstituted 1,2,6-thiadiazine 1,1-dioxides 123 ean exist in three possible tautomerie forms 2H- 123a, 6H- 123b, and AH- 123c (Seheme 33). 

It was shown that, exeept in the eases of 4,4-disubstituted derivatives with the fixed 123c form, nonfunetionalized thiadiazine 1,1-dioxides exist as tautomerie mixtures of 2H (123a) and 6H (123b) tautomers (70CRV593 82JOC536). As... 

Tautomeric,/, tautomerism, tautomery. Tautopf, m. condensing pot steam trap. Taxation,/. = Taxierung. 

Lactame ergeben mit Hydriden den Carbonsaure-amiden ahnliche Reduktionspro-dukte (s. S. 230). Der cyclischen Struktur entsprechend werden cyclische a-Hydroxy-amine und Amine, sowie unter Aufspaltung des Lactam-Ringes co-Amino-alde-hyde und [Pg.244]

Es wurde kein Deuterium im Benzaldehyd gefunden das Alanin enthielt jedoch zwei Atomaquivalente davon, wahrscheinlich in der Methylengruppe. Das laBt sich durch folgende Tautomerie erklaren CH3 CHa... 

Die cis- und trans-Formen der Glutaconsaure sind ein Beispiel fiir eine Tautomerie, bei der aus Grunden der Symmetrie die beiden tauto-meren Formen identisch sind. 

Nach Evans, Rydon und Briscoe (74) sind beim Austausch dieser Sauren in DsO in Gegenwart von iiberschussigem Alkali drei Wasserstoff-atome an der Tautomerie beteiligt. Es wird angenommen, daB die Reaktion iiber ein mesomeres Anion verlauft. 

The three memoirs are Prevost and Kirrmann, "Essai d une theorie ionique des reactions organiques Premier memoire," Bull.SCF 49 (1931) 194243 "Essai. . . Deuxieme memoire," Bull.SCF 49 (1931) 13091368 and "La tautomerie anneau-chaine, et la notion de synionie. Troisieme communication sur la theorie ionique des reactions organiques," Bull.SCF 53 (1933) 253260 quotation from 1931, 194. 

Eistert, Bernhard. Tautomerie undMesomerie Gleichgewicht und Resonanz. Stuttgart F. Enke, 1938. 

La tautomerie anneau-chaine, et la notion de synionie Troisieme communication sur la theorie ionique des reactions organiques." Bull.SCF 53 (1933) 253260. 

Thorpe, Jocelyn, and C. K. Ingold. "Quelques nouveaux aspects de la tautomerie par MM. Jocelyn Field Thorpe et Christopher Kelk Ingold." Bull.SCF 33 (1923) 13421391. 

H. ScHOLz u. E. Frobel Beziehungen zwischen Aciditat und Tautomerie. 

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