Next, we study the relative energetics of Fe(III)-OH isomers, because it has been suggested that isomerization of the Fe(III)-OH intermediate could selectively favor substrate halogenation over hydroxylation during the substrate rebound reaction, meaning that a species that was limited in its ability to isomerize would lead primarily to hydroxylated products in the absence of other selectivity-determining mechanisms. We find that the relative energetic ordering of most Fe(III)-OH isomers is consistent across all halides with small energetic differences of ca. 1 kcal/mol for some isomers as a result of slightly different optimized geometries (Figure and Supporting Information Table and Figure ). The most stable bidentate succinate isomer with axial halide and equatorial OH is strongly preferred over monodentate isomers across all halides by ca. 5-9 kcal/mol (Figure ). This suggests a potential difficulty in isomerization (see calculation of barriers in Sec. 4.3) of the most stable Fe(III)-OH isomer, implying that selective halogenation succ., ax. oxo, eq. X could be expected to take place only when the substrate is positioned more proximal to the halide by second-sphere interactions or the isomerization takes place prior to HAT.