ИСТИНА

Radical cations (RC) of various oxiranes were generated in freonic matrices (CFCl3, CF2ClCFCl2, CF3CCl3) at 77 K by means of x-ray irradiation. The yielded species were analysed by means of EPR- and UV/Vis spectroscopy to determine the characteristics of individual intermediates (ε, λmax, hfc constants) and their photoinduced reactions (φ). DFT calculations of geometries and magnetic resonance parameters were employed to assign the RC and the products of their transformations to certain structures. RC derived from oxiranes exhibit widely different behaviour in terms of photochemistry, both in their reaction mechanisms and the values of the underlying quantum yields. Smaller oxirane RC (methyloxirane, 2,3-dimethyloxirane) can undergo reversible photocyclization when photolysed at different wavelengths. This is untrue for 2,2-dimethyloxirane RC, for which the “anchor” geminal methyl groups hinder rotatory mechanisms (hence, for the completely substituted tetramethyloxirane RC, no cyclic RC can be yielded radiolytically or photolytically). Charge transfer occurs in the case of the trimethyloxirane RC, while the sterically hindered cyclohexene oxide RC extracts H+ under the action of light. A similar mechanism might be ascribed to the transformation of the more rigid cyclopentene oxide RC, although this requires further investigation. This work has been performed with financial support granted by the Russian Foundation for Basic Research (project 16-03-00029).