HYDROGEN TRANSFER FROM KETYL RADICALS TO NITROXYL RADICALS

Article abstract of DOI:10.1007/BF00961676

The transfer of an H atom from a ketyl radical (KR) to a nitroxyl radical is the sole reaction occuring between benzophenone or acetone KR and nitroxyl radicals (NR).The rate constants (k_H) of the reaction of the KR of substituted benzophenones with the NR - 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl and 4-oxo-2,2,6,6-tetramethylpiperidine-1-oxyl in various solvents were measured by the pulse photolysis method.In low-viscosity solvents (up to 1-2 cP), the values of k_H are not limited by the diffusion of the reagents.The k_H values decrease with increase in the Hammet's ?-constants of the substituents in the KR and with decrease in the reduction potential of the NR, which indicates a charge transfer from the KR to NR in the transition state of the reaction.A cyclic structure was proposed for the transition state.The reaction is characterized by a low isotopic effect (k_H/k_D = 1.4-1.5).The dependence of logk_H on the solvation parameter of the solvent E_t(30) is V-shaped in character.