It is known that fluoride-bound halogenase variants of the engineered enzyme SadX solely hydroxylate, whereas chloride-bound variants can both chlorinate and hydroxylate substrates , but the lack of strong differences in energetics we previously identified and further expand upon this work motivates investigation into alternative explanations for this difference in reactivity. For example, isomerization has been invoked to rationalize selectivity of some albeit not all non-heme iron halogenases. In the cases where it has been motivated, such as cases like WelO5 where the substrate in the active site would be distant from the donating halogen in the absence of isomerization , isomerization of the active site after high-valent metal-oxo formation has been suggested as a key factor in the selective C-H halogenation carried out by non-heme Fe(II) enzymes . In particular, prior experimental and computational studies suggested that the key intermediates formed during the catalytic cycle, i.e., Fe(IV)=O and Fe(III)-OH, could isomerize to favor selective halogenation over hydroxylation by positioning the rebounding substrate radical closer to the halogen. While the relative favorability of Fe(IV)=O and Fe(III)-OH isomers in chloride intermediates has been investigated in prior studies, it is not known whether other halogen species exhibit different preferences. Therefore, to identify the ground spin states and to understand the relative energetics and stabilities of isomers of Fe(IV)=O and Fe(III)-OH intermediates, we study active site models of these intermediates and their isomers across all three halides, i.e., fluoride, chloride, and bromide, in all possible spin states (Supporting Information Table and Figure ). Across all halides, we find that all isomers of both studied intermediates have HS ground states (Supporting Information Table ). Furthermore, the HS state is strongly preferred over IS and LS states for all species, and the HS ground states have longer bonds in most intermediates in comparison to the LS states (Supporting Information Tables ).