The abstraction of hydrogen from methane on the terminal iron-oxo group in the ferryl Fe-IV=O and oxyl Fe-III-O-center dot states, the hydrogen peroxide group Fe-OOH and the peroxo group Fe-OO-Fe created in iron hydroxide was modeled by means of the density functional theory. The active groups were built using the Fe4O4(OH)(4) starting complex having one hydrogen removed imitating the effect of the external oxidizer. Among considered groups the oxyl group is predicted to have the highest reactivity. A clear distinction in reactivity between the Fe-III-O-center dot and Fe-IV=O quasi-degenerate states has been attributed to the sign of terminal oxygen spin polarization. (C) 2015 Elsevier B.V. All rights reserved.