Sigma complexes in the pyrimidine series. 4. Investigation of the electronic absorption spectra of anionic sigma complexes of 5-nitropyrimidine

The electronic absorption spectra of sigma complexes of the Meisenheimer type, viz., the anions of potassium salts of 4H-5-nitro-4-acetonylpyrimidines, were investigated. The 5-nitropyrimidine molecule and its sigma complex involving the 4 position were subjected to quantum-chemical calculation by the simple MO LCAO method. It is shown that it is expedient to use the Forster-Dewar-Knott rule for the study of the electronic spectra of the indicated sigma complexes.See [16] for Communication 3.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1260–1263, September, 1981.