Isomerization of the reactive Fe(IV)=O and Fe(III)-OH intermediates, in combination with substrate positioning , is believed to play an important role in reaction selectivity of non-heme Fe(II) enzymes. Due to the fleeting nature of these intermediates, vanadyl mimics are commonly used in experiments to understand the structure of these intermediates. Evaluating substrate distances and angles for the preferred M(IV)=O and M(III)-OH isomers (M = Fe, V) can help us better understand the reliability of vanadyl mimics of native non-heme iron enzymes as well as the enzyme's hydroxylation activity.