Photochemical and Thermal Stability of 1,4-Thioxane and Thiomorpholine Radical Cations in Low-Temperature Freons: A Quantum-Chemical Rationale

A computational study of six-membered radical cations of 1,4-thioxane and thiomorpholine using density functional theory methods (DFT and TD DFT) shows that the relatively high thermodynamic stability of the “chair” conformation and the asymmetric distribution of spin and charge density may explain the absence of thermal transformations up to the matrix melting temperature and photochemical transformations in the visible region for these species, in contrast to the related radical cations of 1,4-dithiane and 1,4-dioxane. The experimental data confirm the stabilization of the aforementioned species in low-temperature freon matrices in the “chair” conformation and the absence of thermal or photochemical transformations in the temperature range of 77–135 K.