The structure of the products was supported by IR, 1 H and 13 C NMR, and HMBC spectroscopy as well as by quantum-chemical calculations. 2-Phenacyl-1H-benzimidazoles in DMSO-d 6 solution were found to display predominantly imino-enamino tautomerism, while their salts were found to display predominantly keto-enol tautomerism.

The unrestricted HF method in the INDO approximation with optimized geometry was used to describe the electronic structure of the hetero-ring of verdazyl and the derivatives of the latter. The results obtained are in good agreement with the experimental EPR spectra of triphenylverdazyl radical and its dipole moment. These data may be a basis for understanding and predicting the chemical properties and reactivity of verdazyl and its derivatives. The changes in spatial and electronic structure of the verdazyl radical and its ions are of great significance for understanding their reactivity in the reactions mentioned above.In this paper we cite the results of quantum investigations of a model heteroring of the verdazyl radical (VJ, its cation (V') and anion (V-) by the INDO method with total geometry optimization [S]. These results make it possible to interpret some specific features of the electronic structure of these compounds and approach well-founded prognoses related to their reactivity.

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