ИСТИНА

Mechanisms of reactions of intermediates (radicals, cation and anion radicals e.t.c.) are of great interest as intermediates play central role in overall description of chemical processes. Cation radicals of small heterocycles and their photoinduced reactions attract attention of researchers yet for some decades. Mechanistic studies mostly rely on EPR and UV-vis spectral data. Though frequently experimental data allow ambiguous interpretation. Here we present study of 1,4-dithiane and aziridine cation radicals photochemistry by means of EPR, UV-vis spectroscopy and DFT, CASSCF, MRPT2 and MRCI calculations. It was found, that in contradiction with literature 1,4-dithiane cation radical undergoes photoisomerization from 1,4-bath conformation to 1,4-twist bath conformation, while in literature the target conformation is considered to be 1,4-chair conformation. Calculated EPR parameters of 1,4-twist bath conformation better suite parameters of the product of photoisomerization. On the other hand calculated geometry of intersection of the first excited state and ground state of 1,4-bath indicates, that the product of photoisomerization is indeed 1,4-twist bath conformation. As for aziridine cation radical in Freon matrices, it was found, that cyclic form spectrum in visible region can be attributed to charge transitions from Freon molecules, while inner spectrum lies mostly in UV region. This explains, why photochemical bond breaking in cyclic form of aziridine cation radical do not take place under photolysis with ~650 nm light, corresponding to the first band in visible spectrum, while photolysis with light with shorter wavelength results in bond breaking.