PNAS Plus Significance Statements

Hydrogen atom abstraction reactivity is a key property of many important biological and synthetic compounds that depends on their protoncoupled reduction potentials. These potentials quantify the ability of species to acquire an electron and proton pair. Intuitively, a species with a higher proton-coupled reduction potential abstracts hydrogen atoms more easily, which translates into a lower reaction barrier. Beyond this classical thermodynamic effect on reactivity, we discovered a significant contribution arising from a factor reflecting propensity for (a)synchronicity in concerted H/e transfers, which stems directly from the reduction potentials and acidity constants of reactants and products. We show that the most synchronous hydrogen atom abstractions tend to pass over the highest barriers, as exemplified by computations on FeO oxidants. (See pp. E10287–E10294.)