Rate coefficients for intramolecular homolytic substitution of oxyacyl radicals at selenium

Ab initio and density functional calculations predict that intramolecular homolytic substitution reactions of oxyacyl radicals at the selenium atom in ω-alkylseleno-substituted radicals proceed via mechanisms that do not involve hypervalent intermediates. When the leaving radical is tert-butyl, energy barriers (ΔG^-) for these reactions range from 27.1 (G3(MP2)-RAD) kJ mol^-1 for the formation of the five-membered cyclic selenocarbonate (6) to 41.5 kJ mol^-1 for the six-membered selenocarbonate (8). G3(MP2)-RAD calculations predict rate coefficients in the order of 10⁵-10⁸ s^-1 and 10²-10 ⁵ s^-1 for the formation of 6 and 8, respectively, at 298.15 K in the gas phase.