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  • Computational Chemistry and Molecular Modeling  (1)
  • Tautomerism  (1)
  • pyrazolones  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Tautomerism of rhodanine (1994)
    Springer
    Structural chemistry 5 (1994), S. 225-231 
    Details
    ISSN: 1572-9001
    Keywords: Tautomerism ; rhodanine ; IR spectra ; ab initio calculations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Semiempirical (MINDO/3, AM1, PM3, MNDO) and ab initio (4-31G and 4-3IG + dAO/S basis sets) calculations on the relative stabilities and structures of the five potential tautomeric forms of rhodanine are reported. It is shown that all methods (excepting PM3) predict as most stable 2-thioxo-4-thiazolidinone. These results correspond to the known experimental data. The infrared spectrum of rhodanine was recorded for the region 4000-150 cm−1, and the characteristic bands were compared with AM1 and 4-31G + dAO/S calculated frequencies. The transition states between five pairs of all possible tautomeric forms of the rhodanine were found by the AM1 method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02275495
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Electronic structure and polarizabilities of some heterocycles: I. Hydroxypyrazoles and related systems (1995)
    Springer
    Molecular engineering 5 (1995), S. 347-361 
    Details
    ISSN: 1572-8951
    Keywords: Polarizabilities ; pyrazolones ; hydroxypyrazoles ; tautomerism ; electronic structure ; excited states ; nonlinear optics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The (hyper)polarizabilities of different tautomer forms of hydroxypyrazoles and pyrazolones have been calculated by the finite-field procedure in the MNDO approximation and the sum of states formalism in the PPP approximation, with all singly- and doubly-excited electronic configurations in the CI method. It was shown that while in the ground electronic state the values of the (hyper) polarizabilities are not essentially different, in the first excited singlet Franck-Condon state an increase of the molecular polarizabilities of some tautomers is observed. This increase is attributed to a specific change in the electronic structure of the excited state, demonstrated by the localization of the electronic transition in the different pyrazolone tautomers. The electron-donor capabilities of phenyl-substituted hydroxypyrazoles and pyrazolones are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01004016
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Tautomerism in 2,2′-bipyridyl-3,3′-diol (1996)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 57 (1996), S. 721-728 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three stable tautomeric forms, dienol (DE), ketoenol (KE), and diketo (DK), of 2,2′-bipyridyl-3,3′-diol BP(OH)2 were found in this study, using the semiempirical AM1 and MNDO-PM3 and ab initio (4-31G basis set) methods. All calculations were carried out without any symmetry restrictions. There is a good agreement between the ab initio calculated and experimentally obtained structural parameters for the DE tautomer. Transition structures, corresponding to the DK → KE and KE → DE processes have also been found. On the basis of the results from the present work, an asynchronous (two-step) DK → KE → DE mechanism of the IPT reaction in BP(OH)2 is proposed. © 1996 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
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