Due to the fact that electronic structure and reactivity are intimately linked, in order to thoroughly appreciate the reactivity of a given system, one has to correctly assign its electronic structure.First, the theoretical methodology about how to analyze the electronic structure of transition metal complexes is presented.1 Then the catalytic mechanism of extradio catecholate dioxygenases2 and Fe(Ⅱ)/α-ketogluatarate-dependent dioxygenases3-6 are discussed.