This Account summarizes research work on the structural aspects and functional features encountered in all major branches of the Gif family of hydrocarbon-oxidizing reagents. Despite assertions by the inventor of Gif chemistry, D. H. R. Barton, to the effect that nonradical pathways could better explain the behavior of Gif systems, detailed experimental investigations provide compelling evidence to support the preponderance of oxygen- and carbon-centered radical chemistry.

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The present investigation explores the functional features of several novel and other previously ill-defined ferrous and ferric complexes of the picolinic acid anion (Pic), which are used to mediate Gif-type oxidation of hydrocarbons by H2O2 Complexes [Fe(Pic)(2)(py)(2)], [Fe(Pic)(3)].0.5py, [Fe2O(Pic)(4)(py)(2)], [Fe-2(mu-OH)(2)(Pic)(4)], and FeCl3 have been employed in oxygenations of adamantane by H2O2 mostly in py/AcOK to reveal that tert- and sec-adamantyl radicals are generated in Gif solutions. The alleged absence of sec-adamantyl radicals from Gif product profiles has been previously interpreted as compelling evidence in support of a non-radical mechanism for the activation of secondary C-H sites in Gif chemistry. The product profile is entirely dictated by trapping of the diffusively free adamantyl radicals, since authentic tert- and sec-adamantyl radicals are shown to partition between dioxygen and protonated pyridine at 4% O-2 (in N-2), or between dioxygen and TEMPO at 100% O-2, in a manner analogous to that observed in Gif oxygenations of adamantane. The low tert/sec selectivity (2.2-4.5) obtained, increasing with increasing dioxygen partial pressure, and the small intramolecular kinetic isotope effect values revealed by employing adamantane-1,3-d(2) (1.06(6) (Ar); 1.73(2) (4% O-2 in N-2)), indicate the presence of an indiscriminate oxidant under inert atmosphere, Coupled to a more selective oxidant at higher partial pressures of dioxygen. Gif oxygenation of DMSO by H2O2 mediated by [Fe(Pic)(2)(py)(2)] provides pyridine-trapped methyl radicals under argon, as expected for the addition reaction of hydroxyl radicals to DMSO. The reaction is progressively inhibited by increasing amounts of EtOH, generating pyridine-captured CH3. CHOH and . CH2CH2OH radicals. Quantification of the DMSO- versus EtOH-derived alkyl radicals affords an estimate of k(EtOH)/k(DMSO) equal to 0.34(3), in reasonable agreement with the kinetics of radiolytically produced hydroxyl radicals (k(EtOH)/k(DMSO) = 0.29). The formation df methyl radicals in Gif oxygenation of DMSO is also supported by the quantitative generation of tert-adamantyl radicals in the presence of 1-iodoadamantane. These results are consistent with the action of hydroxyl radicals in Gif oxygenations by Fe-II/III/H2O2 (Ar), most likely coupled to substrate-centered alkoxyl radicals under O-2. The oxygen-centered radicals perform H-atom abstractions from Gif substrates to generate diffusively free carbon-centered radicals, in accord with previously reported findings.