First evidence for the production of OH radicals by carbonyl oxides in solution phase – A DFT investigation

Dimesitylketone O-oxide (1) rearranges in solution to yield the alcohol 2-methylhydroxy-pentamethylbenzophenone (5) and dimesitylketone (6). DFT-B3LYP/cc-pVTZ calculations reveal that H migration from an o-methyl group to the terminal O atom of the COO unit of 1 rather than the isomerization of 1 is energetically the most favorable process. Calculated activation enthalpies (gas phase: 12.8 kcal/mol; CH3CN solution: 12.4 kcal/mol) are in excellent agreement with measured activation enthalpies (CFCl3 solution: 13.2±0.2 kcal/mol; CH3CN solution: 12.5±0.3 kcal/mol). The hydroperoxide formed by H migration decomposes to a OH and a benzyl radical. Recombination in the solvent cage leads to alcohol 5 while diffusion of OH out of the solvent cage yields 6.