On the other hand, the theoretical interpretation of this 2PCET between catechol (benzene-1,2-diol, ortho H2Q) and O2 •-was investigated by Quintero-Saumeth et al. using DFT calculations and cluster-coupled methods. Their careful work established a reaction scheme in which this reaction proceeds in three elementary steps, (i) formation of the prereactive complex (PRC) from the free reactants (FR), (ii) intra-complex 2PCET forming the product complex (PC) via a transition state (TS), and (iii) dissociation of the product complex yielding the free products (FP).