These fundamental insights have broad implications for developing new strategies to activate C-H bonds, specifically by designing systems with shorter equilibrium proton donor-acceptor distances. This additional effect arising from the strong dependence of proton transfer on the proton donor-acceptor distance provides an explanation for the greater sensitivity of the rate constant to the carboxylate basicity than to the redox potential of the oxidant. In addition to increasing the driving force for proton transfer, enhancing the basicity of the carboxylate also decreases the equilibrium proton donor-acceptor distance, thereby facilitating the sampling of shorter proton donor-acceptor distances. Herein a vibronically nonadiabatic PCET theory is used to explain how changing the driving force for the electron and proton transfer components of the reaction through varying the oxidant and the substituent, respectively, impacts the PCET rate constant. Experiments showed that the rate constants are much more sensitive to the carboxylate basicity than to the redox potential of the oxidant. 27 × 10 7 times faster than the dissociation rate in free water and that the proton transfer reactions are capable of explaining the enhanced water dissociation if there is always enough water in the transition region. The electron transfer driving force depends predominantly on the oxidant, and the proton transfer driving force depends mainly on the basicity of the carboxylate, which is influenced by the substituent on the benzoate fragment. The driving force for the migration of protons and hydroxyl ions is U ex. As noted, the driving force for facilitated diffusion is concentration, meaning that in facilitated diffusion, materials will only move from a higher concentration to a lower concentration and that at the end of the process, the concentration of materials on each side of a bilayer will be equal (Figure 3.28). This mechanism is based on multi-site concerted proton-coupled electron transfer (PCET) involving intermolecular electron transfer to an outer-sphere oxidant coupled to intramolecular proton transfer to a well-positioned proton acceptor. This mechanism is based on multi-site concerted proton-coupled electron transfer (PCET) involving intermolecular electron transfer to an outer-sphere oxidant coupled to intramolecular proton transfer to a well-positioned proton acceptor. Calculations using vibronically nonadiabatic P CETtheory yield rate constants forsimultaneous tunneling of the electron and proton that account for the results. Recently selective C-H bond cleavage under mild conditions with weak oxidants was reported for fluorenyl-benzoates. dependence on the driving force upon changing pyridine substituents and the solvent.
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