The tight control of the photochemical hydrocarbon oxidations results from access to a low-energy reaction path. This occurrence, coupled with the confinement imposed by the zeolite cage, prevents random radical coupling reactions and homolytic fragmentation of the primary products. Specifically, there is no homolytic O-O bond rupture of the hydroperoxide intermediates, which would lead to the formation of OH and alkoxy radicals.
Alkoxy radicals destroy the selectivity of the thermal autooxidation of small hydrocarbons.
Therefore, the method of hydrocarbon oxidation by O 2 with visible light is inherently stable against overoxidation. Only in alkanes are the ionization potentials of the carbonyl products lower than those of the parent hydrocarbons. However, we have not yet observed overoxidation under visible light, even in these cases.