Electron configuration of the [FeO](2+) group in the H-abstraction from methane: oxyl versus ferryl

This account presents author’s opinion on the mechanism of the H-abstraction from methane by the FeO group. In the course of reaction with hydrogen, the Fe-O bond in the ferryl configuration becomes elongated causing transfer of the spin-up electron from one of doubly occupied bonding orbitals leaving behind single spin-down electron on oxygen. This oxygen in so-formed oxyl configuration of the FeO moiety then easily accept the spin-up hydrogen atom from methane in the same way as the radical-localized oxygen does. This mechanism is compared with the scheme in which the hydrogen is accepted by low-lying unoccupied antibonding orbital in the ferryl configuration.