Proton Coupled Electron Transfer (PCET) mechanisms include all kinds of reactions where concurrent/stepwise processes are involved. Unraveling the distinctive character of a given mechanism is therefore a issue of importance, as concerted mechanisms lead to formation of products, avoiding the formation of high energy intermediates and are important for catalysis, while stepwise steps allow explaining the reactivity where radical species (either neutral or charged), can be invoked. Therefore, studies are not only directed to distinguish between both mechanistic alternatives, but to rationalize their significance in the reactivity of molecules and aggregates. For this purpose, simple trends using model organic compounds have been studied and allow to identify the structural characteristics that a given species must bear to induce any path. Within the workgroup, systematic analysis with series of nitro aromatic compounds [1,2] where Electron Transfer Controlled Hydrogen Bonding (a specific type of PCET process), show the influence of both the basicity of the electrogenerated anion radical and the acidity of the proton donor, describing the trends using descriptors of reactivity derived from changes in the local density of the molecule [3]. Using this approach, we have been able to analyze critical parameters where Hydrogen Bonding can lead to Proton Transfer, thus probably becoming concerted proton transfers. Results are therefore discussed in this work, along with the theoretical analysis described, its own limitations and some recent extensions for multiple-bodies approaches. Also, experimental changed where self-protonation occurs are presented, where we have been able to identify the "non-innocent" character of hydrogen bonding donors within the structures, leading to prior of forward hydrogen bonding interactions. Finally, some results of the influence of hydrogen bonding in the changes in electron transfer entropy are presented.

[1] Martínez-González, E.; C. Frontana, J. Org. Chem. 2014, 79, 1131-1137

[2] Martínez-González, E.; Armendáriz-Vidales, G.; Ascenso, J. R.; Marcos, P. M.; Frontana C. J. Org. Chem. 2015, 80, 4581-4589

[3] Gázquez, J. L.; Cedillo, A.; Vela, A. J. Phys Chem. A. 2007, 111, 1966-1970