The effect of leaving radical on the formation of tetrahydroselenophene by S_Hi ring closure: An experimental and computational study

Competition kinetic studies augmented with laser-flash photolysis and high-level computational techniques [G3(MP2)-RAD], with [COSMO-RS, SMD] and without solvent correction, provide kinetic parameters for the ring closures of a series of 4-(alkylseleno)butyl radicals 1. At 22 °C rate constants (k_c) that lie between 10⁴-10⁷ s^-1 were determined experimentally and correlate with expectations based on leaving group ability. Activation energies (E_act) were determined to lie between 10.6 (R = Ph₂CH) and 28.0 (R = n-Bu) kJ mol^-1, while log(A/s^-1) values were generally between 9 and 10 in benzene. Computationally determined rate constants were in good-to-excellent agreement with those determined experimentally, with the COSMO-RS solvation model providing values that more closely resemble those from experiment than SMD.