acid cannot be formed because of its rapid disproportionation, but its third acid dissociation constant has been estimated by pulse radiolysis techniques: HMnO MnO + H+ pK''a = Cyclic esters of hypomanganic acid are thought to be intermediates in the oxidation of alkenes by permanganate. See also Dimanganite, a manganate(III) anion Manganate or manganate(VI), Permanganate or manganate(VII), References Manganese(V) compounds Transition metal oxyanions