Considering the acidic experimental conditions (pH=1.5), a further justification of the most likely hydroquinone's oxidation process in the presence of Al 3+ can be done. Despite in Q10 we have considered reagent [Al(EtOH) 5 (QH -)] 2+ , it can not be formed directly by [Al(EtOH) 6 ] 3+ + QH -because at pH=1.5 deprotonated hydroquinones are not present in solution. Instead, it may come from the deprotonation of other Al 3+ complex such as [Al(EtOH) 5 (QH 2 )] 3+ through a multistep process as it is shown in Figure ). [Al(EtOH) 5 (QH 2 )] 3+ is a high energy complex (∆G of 11.8 kcal/mol, reported in Table ), which acts as an intermediate preventing the formation of [Al(EtOH) 5 (QH -)] 2+ and precluding reactions Q8, Q9, and Q10 to be feasible oxidation processes. A similar situation may happen for Q4. Q4 reaction entails two unfavourable processes together (ethanol deprotonation and hydroquinone PCET), which involves that the formation of an endergonic intermediate is highly likely (like the ones of Q3 or Q1) through a multi-step reaction mechanism (see Figure ). The high energy necessary to form these intermediates prevents the formation of [Al(EtOH) 4 (EtO -)(QH•)] 2+ through them.