THERMOCHEMISTRY OF ORGANIC POLYOXIDES AND THEIR FREE-RADICALS

Using recently reported data on the kinetics of decomposition of species R2O3 and R2O4 in solution (R = t-Bu, D) and in the gas phase (R = SF5), it is possible to show that the difference, ΔH°f(O-(O)2) - ΔH°f(RO2) = 14.5 - ΔH°f(RO) where the first term represents the contribution of the group O-(O)2 to the heats of formation of polyoxides. Since, for many alkoxy radicals (RO), heats of formation are now known with good accuracy, either one value of ΔH°f(RO2) or one absolute value of ΔH°f(O-(O)2) from ΔH°f of any polyoxide will serve to fix the other. The assumption DH°(RO2-H) = DH°(HO2-H) = 89.6 ± 2 kcal/mol is shown to be in good agreement with independent solution measurements and fixes the group value ΔH°f(O-(O)2) = 16.8 ± 2 kcal/mol, an appreciable improvement over earlier deductions. New values derived from this are listed for ΔH°f of R2On and ROn (n ≥ 2) where R = H, Me, and t-Bu. The radical group values ΔH°f[O-(O)(H)] = 5.0 and ΔH°f[O-(O)(C)] = 16.4 kcal/mol are derived from the data. Group additivity permits the calculation of ΔH°f for other polyoxy radicals. © 1979 American Chemical Society.