Reactions of aromatic and aliphatic hydrocarbons with a new reagent system, Fe (CH₃CN)²⁺₆-H₂O₂-Ac₂O in CH₃CN, gave oxygenation products with fairly high reaction efficiency (Tables I and II) compared to known reagent systems used as enzyme models for mono-oxygenases. Investigations of the mechanism of these reactions indicated the involvement of either complex C, Fe^IV (OH) (OAc)²⁺, or complex D, Fe^IV (OAc)²⁺₂, depending on the organic substrate.