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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Structural chemistry 5 (1994), S. 225-231 
    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
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  • 2
    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
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