We next studied isomerization energy landscapes of Fe(IV)=O intermediates for all three halides to assess their likelihood of interconversion. We compare the active site isomerization across fluoride, chloride, and bromide intermediates to understand any differences in isomerization barriers and preferred orientation of oxo/halide ligands in intermediates of the catalytic cycle. We study two isomerization reaction coordinates (RCs) corresponding to the isomerization of a) halide and b) oxo ligands from axial to equatorial positions with both monodentate and bidentate succinate isomers. As previously discussed, we expect isomerization of Fe(IV)=O intermediates to be favored when the active site has a monodentate succinate configuration to ensure the needed coordination flexibility within the active site to enable isomerization. Moreover, monodentate metal-oxo isomers are only slightly less favorable than the bidentate isomers by ca. 3 kcal/mol (Figure ).