Oxo-iron(V) species have been implicated in the catalytic cycle of the Rieske dioxygenase. Their synthetic analog, [Fe-V(O)(OC(O)CH3)(PyNMe3)](2+) (1, PyNMe3 = 3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene-3,6,9-trimethyl), derived from the O-O bond cleavage of its acetylperoxo iron(III) precursor, has been shown experimentally to perform regio- and stereoselective C-H and C=C bond functionalization. However, its structure-activity relation is poorly understood. Herein we present a detailed electronic-structure and spectroscopic analysis of complex 1 along with well-characterized oxo-iron(V) complexes, [Fe-V(O)(TAML)](-) (2, TAML = tetraamido macrocyclic ligand), [Fe-V(O)(TMC)(NC(O)CH3)](+) (4, TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), and [Fe-V(O)(TMC)(NC(OH)CH3)](2+) (4-H+), using wave function-based multireference complete active-space self-consistent field calculations. Our results reveal that the x/y anisotropy of the Fe-57 A-matrix is not a reliable spectroscopic marker to identify oxo-iron(V) species and that the drastically different A(x) and A(y) values determined for complexes 1, 4, and 4-H+ have distinctive origins compared to complex 2, a genuine oxo-iron(V) species. Complex 1, in fact, has a dominant character of [Fe-IV(O center dot center dot center dot OC(O)CH3)(2-center dot)](2+), i.e., an S-Fe = 1 iron(IV) center antiferromagnetically coupled to an O-O sigma* radical, where the O-O bond has not been completely broken. Complex 4 is best described as a triplet ferryl unit that strongly interacts with the trans acetylimidyl radical in an antiferromagnetic fashion, [Fe-IV(O)(N-center dot=C(O-)CH3)](+). Complex 4-H+ features a similar electronic structure, [Fe-IV(O)(N-center dot=C(OH)CH3)](2+). Owing to the remaining approximate half sigma-bond in the O-O moiety, complex 1 can arrange two electron-accepting orbitals (alpha sigma*O-O and beta Fe-d(xz)) in such a way that both orbitals can simultaneously interact with the doubly occupied electron-donating orbitals (sigma(C-H) or pi(C-C)). Hence, complex 1 can promote a concerted yet asynchronous two-electron oxidation of the C-H and C=C bonds, which nicely explains the stereospecificity observed for complex 1 and the related species.