The one-electron redox potentials of QH 2 , Me 4 QH 2 , and DPPH• (Figure ) with and without the presence of the Al 3+ ion in solution were studied computationally and compared with the experimental redox potentials presented in ref. 20 in order to validate the level of theory and results. Experimental values are summarized in Table . Considering the contrary relation between redox potentials and free energies ( E=-∆G/nF ), experimental results exhibit that the oneelectron donating ability of hydroquinones decreases with the presence of Al 3+ , while the electron-accepting ability of DPPH• increases. However, the reduction of DPPH• is more promoted rather than the oxidation of hydroquinones impeded, and as a consequence, the global redox DPPH• radical scavenging reaction of hydroquinones in the hydroalcoholic medium evolves from non-spontaneous (E reac < 0) to spontaneous (E reac > 0) by the presence of Al . Both electron transfer (ET) and PCET oxidation and reduction processes were analyzed. For hydroquinones (i.e. QH 2 and Me 4 QH 2 ), the computed oxidation potentials of PCET reactions are clearly the ones that agree with experimental values (reactions b and f). E ox (reac. b) highly matches with the experimental value and E ox (reac. f) differs 0.17 eV from the experiment, which lies in the accepted error range. Overall, this allow us to establish that the oneelectron oxidation processes measured for hydroquinones are PCET. In contrast, the assignation is unclear for DPPH• because both ET and PCET computed reduction potentials have values close to the experiment, differing up to 0.09 eV.