We found that the key to successfully predicting the E red. and E 0 values is the LUMO of products participating in the oxidation reactions (See Figure ). Prediction of pK a is strongly dependent on HOMOs. Overall, as shown in Figure , the reactant's HOMO and the product's LUMO participating in the oxidation reactions are inversely correlated to E red. and E 0 . Based on Koopmans' theorem, the ionization energy of molecules inversely correlates with their negative HOMO energies. There have been reports of a similar trend in recent years.