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Stable Tautomer (stable + tautomer)
Selected AbstractsSolid-State Structure and Tautomerism of 2-Aminotroponimines Studied by X-ray Crystallography and Multinuclear NMR SpectroscopyEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 21 2004Rosa M. Claramunt Abstract Structural studies in the solid state by X-ray crystallography and by 13C and 15N CPMAS NMR spectroscopy carried out on a series of 2-aminotroponimine derivatives 2,5 has allowed to establish the existence of hydrogen bonding and to determine the most stable tautomer. Almost all the structures reflect the classical double-well potential function for the N,H···N hydrogen bonds. Only in the case of the compound N -(pyrrol-1-yl)-2-(pyrrol-1-ylamino)troponimine (5) the crystal structure shows two independent molecules, one with a classical hydrogen bond and another with either a single-well or a low-barrier hydrogen bond. The structure of this compound is discussed with the use of the solid-state NMR spectroscopic data. 2-Aminotropones, as intermediates to the 2-aminotroponimines, show the oxo-tautomer as the stable form. B3LYP/6-31G* calculations are used to rationalise the experimental results. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Efficient Enantioselective Syntheses of Sertraline, 2-Epicatalponol and Catalponol from Tetralin-1,4-dioneADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2010Alvaro Enriquez Garcia Abstract Tetralin-1,4-dione, the stable tautomer of dihydroxynaphthalene, was reduced with catecholborane in the presence of 3,3-diphenyl-1-butyltetrahydro-3H -pyrrolo[1,2- c][1,3,2]oxazaborole as catalyst to give enantiomerically highly enriched 4-hydroxy-1-tetralone (99% ee) in an efficient one-pot procedure. The R -enantiomer provided a rapid access to sertraline while the S -enantiomer was converted into 2-epicatalponol and catalponol. A more selective enantioselective route to the antithermitic catalponol made use of the planar chiral tricarbonylchromium complex of hydroxytetralone. Its precursor chromium(tricarbonyl)[,6 -(1-4,4a,8a)-tetralin-5,8-dione] was obtained via direct complexation of 1,4-dihydroxynaphthalene using chromium(tricarbonyl)- tris(ammonia) and boron trifluoride etherate as source of the chromium(tricarbonyl) fragment. Enolate prenylation was best carried out in the presence of a tetraamine ligand. Complete inversion of the stereogenic center bearing the prenyl group of the initially obtained tetralone complex was achieved via enolate formation followed by protonation. [source] Gas-phase tautomers of protonated 1-methylcytosine.JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 11 2005Preparation, dissociation mechanisms, energetics Abstract Tautomers of 1-methylcytosine that are protonated at N-3 (1+) and C-5 (2+) have been specifically synthesized in the gas phase and characterized by tandem mass spectrometry and quantum chemical calculations. Ion 1+ is the most stable tautomer in aqueous and methanol solution and is likely to be formed by electrospray ionization of 1-methylcytosine and transferred in the gas phase. Gas-phase protonation of 1-methylcytosine produces a mixture of 1+ and the O-2-protonated tautomer (3+), which are nearly isoenergetic. Dissociative ionization of 6-ethyl-5,6-dihydro-1-methylcytosine selectively forms isomer 2+. Upon collisional activation, ions 1+ and 3+ dissociate by loss of ammonia and [C,H,N,O], whose mechanisms have been established by deuterium labeling and ab initio calculations. The main dissociations of 2+ following collisional activation are losses of CH2CNH and HNCO. The mechanisms of these dissociations have been elucidated by deuterium labeling and theoretical calculations. Copyright © 2005 John Wiley & Sons, Ltd. [source] The Tautomeric Forms of Cyameluric Acid Derivatives,CHEMISTRY - A EUROPEAN JOURNAL, Issue 4 2007Nadia Abstract The tautomerism of cyameluric acid C6N7O3H3 (1,a), cyamelurates and other heptazine derivatives has recently been studied by several theoretical investigations. In this experimental study we prepared stannyl and silyl derivatives of cyameluric acid (1,a): C6N7O3[Sn(C4H9)3]3 (3,a), C6N7O3[Sn(C2H5)3]3 (3,b), and C6N7O3[Si(CH3)3]3 (4). In order to investigate the structure of 1,a the mono- and dipotassium cyamelurate hydrates K(C6N7O3H2),2,H2O (5) and K2(C6N7O3H),1,H2O (6) were synthesized by UV/Vis-controlled titration of a potassium cyamelurate solution with aqueous hydrochloric acid. Compounds 3,6 were characterized by FTIR and solid-state NMR spectroscopy as well as simultaneous thermal analysis (TGA, DTA). The single crystal X-ray structures of the salts 5 and 6 show that the hydrogen atoms in both anions are localized on the peripheral nitrogen atoms. This indicates,in combination with the solid-state NMR studies,that the most stable tautomer of solid 1,a is the triketo form with C3h symmetry. However, derivatives of both the hydroxyl and the amido tautomers may be formed depending on the substituent atoms: The spectroscopic data and single crystal structures of compounds C6N7O3[Si(CH3)3]3 (4) and the solvate C6N7O3[Sn(C2H5)3]3,C2H4Cl2 (3,b,) show that the former is derived from the symmetric trihydroxy form of 1,a, while 3,b, crystallizes as a chain-like polymer, which contains the tin atoms as multifunctional building blocks, that is, bridging pentacoordinated Et3SnO2 and Et3SnON units as well as non-bridging four-coordinated Et3SnN units. The cyameluric nucleus is part of the polymeric chains of C6N7O3[Sn(C2H5)3]3,C2H4Cl2 (3,b,), by the action of both tautomeric forms of cyameluric acid, the amide and the ester form. [source] | ||||||||||