The nature of the bands of the electronic absorption spectra of acid solutions of aromatic α,β-unsaturated ketones

The electronic absorption spectra of 34 unsaturated ketones were measured in solutions of 93% sulfuric acid. The curves of the absorption of the hydroxycarbonium ions formed as a result of protonation of the investigated compounds in sulfuric acid solutions, are characterized by the presence of two intense bands of the -^* type in the region of 330–630 nm. The nature of the bands of the investigated compounds is discussed on the basis of the calculated data, obtained according to the PPP method, with an estimation of the localization and charge transfer numbers of the electronic transitions on individual fragments. According to the data of calculation and graphical analysis it was shown that the long-wave band in a series of derivatives of diphenylmethane and diphenyl oxide (I, II) should be assigned to the protonated cinnamoyl (C) fragment, while the second (short-wave) band should be assigned to the protonated acetophenone (A) fragment. The long-wave band in the series of derivatives of diphenyl sulfide, diphenylamine, and N-methyldiphenylamine (III–V) was assigned to the protonated acetophenone fragment. The resonance, dipole-dipole and exchange interactions of the fragments A and C is analyzed, and an attempt was undertaken to distinguish various types of interactions.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 3, pp. 321–328, May–June, 1985.