Abstract
The electron densities, the lower singlet-singlet transitions, and the diamagnetic characteristics were calculated on the basis of the semiempirical self-consistent-field method for a number of oxazolium and variously substituted oxazolium cations. The results were found to be in agreement with the available experimental data. The parameters of the nitrogen atom in the oxazolium cations were adopted within the framework of a unified parametrization that unites the pyridine, pyrrole, and immonium nitrogen atoms. It was found that over a broad range of structural changes in the oxazolium cation the maximum positive charge is found in the 2 position; this determines the site of nucleophilic addition in reactions involving opening and recyclization of these heterocycles. It was shown that the phenyl substituent attached to the nitrogen atom is least conjugated with the heteroring as compared with the other positions in the oxazolium ring; as a consequence of this, the smallest bathochromic shift of the long-wave absorption band of the UV spectrum is observed in the series of phenyl-substituted oxazolium salts, and the N-methyl group markedly shifts the spectrum to the short-wave region. The scale of aromaticity of the investigated compounds, according to which the azolium cations are less aromatic than the corresponding bases, is given.
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Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1186–1191, September, 1977.
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Vysotskii, Y.B., Kovach, N.A. & Shvaika, O.P. Investigation of oxazolium compounds by the self-consistent-field MO LCAO method. Chem Heterocycl Compd 13, 954–959 (1977). https://doi.org/10.1007/BF00472445
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DOI: https://doi.org/10.1007/BF00472445