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1Author    Sn Bakalova, A. Georgieva, P. Nikolov, E. StanoevaRequires cookie*
 Title    Dihydronaphthalenone Carboxylates - Spectral Characteristics and Structure  
 Abstract    The absorption and luminescence characteristics of a group of newly synthesized methyl esters of 2-alkyl (p-substituted-aryl) -aminomethylene-3,4-dihydro-l(2 H)-naphthalenone-4-carboxylic acids have been investigated. The studied compounds may exist in three tautomeric forms. On the basis of comparison of their electronic spectra to those of similar substances, the observed substituent effect on the position of the UV-VIS absorption bands, the IR spectra and the results of PPP-SCF-CI quantum-chemical calculations it is concluded that the keto tautomer predominates in solution. 
  Reference    Z. Naturforsch. 52a, 457—461 (1997); received December 31 1996 
  Published    1997 
  Keywords    Electronic spectra, Tautomerism, Dihydronaphthalenone carboxylates 
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 TEI-XML for    default:Reihe_A/52/ZNA-1997-52a-0457.pdf 
 Identifier    ZNA-1997-52a-0457 
 Volume    52 
2Author    Requires cookie*
 Title      
 Abstract    The reaction of imines with various electrophiles have afforded only N-alkylated products, contrary to earlier reports. While a large amount of work has been done on the synthetic applications of tertiary enamines, pioneered by S t o r k and coworkers1*2, less is known about the scope of similar applicability of secondary enamines. Secondary enamines predo­ minantly exist in the imino form both in aliphatic and in cyclic compounds except in cases where the R. R I tertiary enamine secondary enamine 
  Reference    (Z. Naturforsch. 30b, 128—131 [1975]; received September 13 1974) 
  Published    1975 
  Keywords    Imines, Enamines, Alkylation, Tautomerism 
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 TEI-XML for    default:Reihe_B/30/ZNB-1975-30b-0128.pdf 
 Identifier    ZNB-1975-30b-0128 
 Volume    30 
3Author    K. C. Dash, A. Schmidpeter++, H. Schmidbaur+Requires cookie*
 Title    Gold Complexes of a P-Coordinate Cyclotriphosphazene [1,2]  
 Abstract    Contrary to the reports on the coordination oi copper (I) to N/P-ambidentate cyclotri-phosphazenes, gold (I), gold (III) and dimethylgoldf 111) chloride are found to become exclusively P-coordinated to the prototype ligand 2-methyl-4,4,6,6-tetraphenylcyclotri-phosphazene (1). The P-H proton is transferred to an adjacent nitrogen atom of the heterocycle. According to temperature dependent NMR spectra, the AuCl and the AuClß complexes are fluxional molecules or ions, resp., with a rapid proton transfer between P-NH-P and P = N-P functions. The behaviour is similar to that of related palladium and platinum complexes, reported previously. 
  Reference    Z. Naturforsch. 35b, 1286—1288 (1980); eingegangen am 9. Juni 1980 
  Published    1980 
  Keywords    Gold Complexes, Cyclotriphosphazenes, N/P-Ambidentate System, Tautomerism 
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 TEI-XML for    default:Reihe_B/35/ZNB-1980-35b-1286.pdf 
 Identifier    ZNB-1980-35b-1286 
 Volume    35 
4Author    Jerzy Sepiol, Zygmunt Kazimierczuk, David ShugarRequires cookie*
 Title    Tautomerism of Isoguanosine and Solvent-Induced Keto-Enol Equilibrium  
 Abstract    Ultraviolet and infrared absorption spectroscopy, in aqueous and non-aqueous media, have been employed to study the tautomerism of 9-substituted isoguanines, including the nucleoside iso­ guanosine. With the aid of a series of model compounds, it was shown that 9-substituted isogua­ nines, and isoguanosine, in aqueous medium are predominantly in the form N (1) H,2-keto-6-amino. In dioxane solution the tautomeric equilibrium is shifted in the direction of the enol form. The shift towards this form is accentuated for those analogues in which the exocyclic amino group is methylated. 
  Reference    (Z. Naturforsch. 31c, 361 [1976]; received May 3 1976) 
  Published    1976 
  Keywords    Isoguanine Analogues, Isoguanosine, Tautomerism, Tautomeric Equilibrium, Solvent Polarity 
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 TEI-XML for    default:Reihe_C/31/ZNC-1976-31c-0361.pdf 
 Identifier    ZNC-1976-31c-0361 
 Volume    31 
5Author    Piotr CysewskiRequires cookie*
 Title    Theoretical Studies on the Tautomeric Properties of Diamino-5-formamidopyrimidines  
 Abstract    The results of theoretical geometry prediction of formamidopyrimidine(fapy)-adenine and fapy-guanine tautomers are presented. Among 54 potential tautomeric structures of fapy-adenine the most stable structure corresponds to the diamino-keto isomer. The solvent effect has insignificant influence on the fapy-adenine tautom ers succession. The fapy-guanine has 172 potential isomers. There are three most stable tautom ers of this guanine derivative, which may exchange the order depending on the polarity of the environment. In vapour the most probable is the 4-enol-6-keto-diamino tautomer, while in water environm ent the 4,6-diketo-diamino isomer is dominant. A more polar solvent stabilises more polar fapy-guanine tauto­ mers. The geometric parameters and point-atomic charges corresponding to most probable tau­ tomers are also supplied. 
  Reference    Z. Naturforsch. 53c, 1027—1036 (1998); received April 20/June 19 1998 
  Published    1998 
  Keywords    Fapy-adenine, Fapy-guanine, Tautomerism, Solvent Effect 
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 TEI-XML for    default:Reihe_C/53/ZNC-1998-53c-1027.pdf 
 Identifier    ZNC-1998-53c-1027 
 Volume    53 
6Author    Latif Rateb, B. Azmy, M. A. Nashed, M. F. IskanderRequires cookie*
 Title      
 Abstract    A series of benzoylacetaldehyde benzoylhydrazones were prepared and characterised. Their UV, IR, and iH NMR spectra suggest the enol-imine structure rather than the keto-imine form of analogous Schiff bases. The pKa values of these aroylhydrazones were also measured and correlated with the Hammet substitution constants. Attempted cyclizations of these open-chain aroylhydrazones afforded the corresponding 5-hydroxy-2-pyrazoline compounds rather than the expected pyrazoles. 
  Reference    Z. Naturforsch. 33b, 1527—1534 (1978); received July 24 1978 
  Published    1978 
  Keywords    Benzoylacetaldehyde Benzoylhydrazone, 5-Hydroxy-2-pyrazolines, UV, Tautomerism, Enol-imines 
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 TEI-XML for    default:Reihe_B/33/ZNB-1978-33b-1527.pdf 
 Identifier    ZNB-1978-33b-1527 
 Volume    33 
7Author    M. Ikko Koskinen3, IlpoM. Utikainenb, Hannu EloaRequires cookie*
 Title    Crystal and Molecular Structure of Aminoguanidine Sulphate, an Important Enzyme Inhibitor and Starting Material of Drug Syntheses  
 Abstract    Aminoguanidine is not only an agent with a variety of pharmacological effects but also an im portant starting material of am idinohydrazone-type drugs and enzyme inhibitors. There­ fore, we have now synthesized am inoguanidine sulphate CN4H 82+.S 0 42~ and determined its structure by single-crystal X-ray diffraction. The doubly protonated (dication) form o f am ino­ guanidine that is present in the sulphate could, in principle, exist in the form of several differ­ ent tautom ers. The crystal studied consisted exclusively of one tautomer: one of the nitrogens of the hydrazine moiety bears three hydrogen atoms while the other one (the one bound to the carbon) bears one hydrogen. The other two nitrogens are bound to two hydrogens each. The predominance of this tautom er can be explained by the very strong resonance in it. The dica­ tion of aminoguanidine is remarkably planar. The hydrogens of the hydrazine moeity are, however, clearly out of the plane of the other atoms. There is a strong hydrogen bond between the proton of the m onoprotonated nitrogen and one sulphate oxygen. This bond obviously causes the deviation of the hydrogen from the plane. The bonds between the carbon atom and the adjecnt nitrogens are essentially equally long, indicating that each bond has approxim ately the same am ount of double bond character. One of the positive charges of the dication is thus delocalized, being shared by all of the atoms of the C N 3 moiety. In this respect, the structure is similar to that of all bis(amidinohydrazones) whose structures have been determined. The other positive charge of aminoguanidine dication is localized at the nitrogen bearing three hydrogens. 
  Reference    Z. Naturforsch. 49b, 556—560 (1994); received December 6 1993 
  Published    1994 
  Keywords    Bis(guanylhydrazones), Diamine Oxidase Inhibitors, Nitric Oxide Synthase Inhibitors, Resonance, Tautomerism 
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 TEI-XML for    default:Reihe_B/49/ZNB-1994-49b-0556.pdf 
 Identifier    ZNB-1994-49b-0556 
 Volume    49 
8Author    Jochen Ellermann, AlfonsA M DemuthRequires cookie*
 Title    Chemistry of Poly functional Molecules, 75 [1] The Reaction of 5-Bromo-uracil with Sodium Diphenylphosphide  
 Abstract    5-Bromo-uracil (1) reacts with sodium diphenylphosphide or a mixture of sodium diphenylphosphide and sodium amide in liquid ammonia to give sodium 5-bromo-uracilate (5 a). From water 5 a crystallizes with one mole H2O yielding 5b. Treatment of 5 a with D2O yields sodium 5-bromo-N-deutero-uracilate-D20 (1/1) (5 c). With chlorodiphenyl-phosphine 5a forms 1-diphenylphosphino-uracil (2). 5a, b, c show N(l)-N(3)-(H/D)-tauto-merism in concentrated D2O solutions already, but in DMSO or Dö-DMSO only in dilute solutions. All the compounds were characterized by infrared, Raman, X H NMR, UV spectra and conductometry. 
  Reference    Z. Naturforsch. 38b, 1568—1574 (1983); eingegangen am 6. Juni/2. August 1983 
  Published    1983 
  Keywords    Sodium 5-Bromo-uracilates, Deutero Derivatives, Tautomerism, NMR Spectra, UV Spectra, Vibrational Spectra 
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 TEI-XML for    default:Reihe_B/38/ZNB-1983-38b-1568.pdf 
 Identifier    ZNB-1983-38b-1568 
 Volume    38