Epoxidation of styrene derivatives, sulfoxidation of thioanisole derivatives, and hydroxylation of toluene derivatives by a nonheme manganese(IV)-oxo complex binding triflic acid, [(N4Py)-Mn-IV(O)](2+)-(HOTf)(2) [1-(H+)(2)], and scandium triflate, [(N4Py)Mn-IV(O)](2+)-(Sc(OTf)(3))(2) [1-(Sc3+)(2)], occur via outer-sphere electron-transfer (OSET) pathways, exhibiting singly unified driving force dependence, enabling one to predict absolute values of the second-order rate constants of these three types of substrate oxidations by the manganese(IV)-oxo complex, using the Marcus theory of electron transfer. When [(N4Py)Mn-IV(O)](2+) (1) was replaced by [(N4Py)Fe-IV(O)](2+) (2), OSET pathways were changed to inner-sphere electron-transfer (ISET) pathways. The difference in the OSET versus ISET pathways is clarified based on the difference in the Lewis basicity of the oxo moieties in 1 and 2.