Tunneling rate constants for intramolecular hydrogen atom transfer reactions in solution

Theoretical aspects of tunneling proton transfer reactions in a polar environment

“…When the solvent is included in standard descriptions, it is imagined to alter the rate via a differential equilibrium solvation of the TS and the reactant, again all within the standard framework recounted above 49, 50–53. But the equilibrium solvation assumption – which requires the solvent motion to be fast compared to the relevant motion of the reacting solutes in the TS region – is completely implausible for the rapid quantum motion of a light proton; indeed, the opposite situation is more appropriate: the solvent is generally slow compared to the proton motion 1–11, 54–69. Most applications of the equilibrium solvation framework use modern multidimensional tunneling techniques to calculate the tunneling ‘correction’ 50–53, 70–78…”

“…In the alternate, nontraditional picture of PT reactions1–18, 54–68 employed within, the reaction is driven by configurational changes in the surrounding (polar) environment – a feature of much modern work on PT reactions,1–18, 54–68 and the reaction activation free energy is largely determined by the environmental reorganization. In this picture, the rapidly vibrating quantum proton follows the environment's slower rearrangement, thereby producing a perspective in terms of the instantaneous proton potential for different environmental arrangements.…”

“…This paper gives an overview of some of the theoretical developments for tunneling proton transfer (PT) reactions, focusing on the efforts in the Hynes group 1–18. PT is of obvious importance in both chemistry and biology,19–23 resulting in the extensive study of PT in solution19–35 and other polar environments, e.g., enzymes 26, 36–39.…”

Excited‐State Proton Transfer via Hydrogen‐Bonded Dimers and Complexes in Condensed Phase

“…One relevant, important issue of current interest is the ESPT-coupled excited-state charge transfer (ESCT) reaction. Some seminal theoretical approaches taken by Hynes and coworkers revealed the key features, with description of the dynamics and electronic structures of non-adiabatic [102][103][104] and adiabatic [105][106][107] intermolecular proton transfer reactions in protic solution. The most recent theoretical advancement has incorporated both solvent reorganization and proton tunnelling through barriers and made the framework resemble electron transfer [102][103][104][105][106][107][108][109][110][111], such that the proton transfer rate k pt can be categorized into two regimes:…”

“…As a result, the proton tunnelling probability varies with respect to types of vibration. Hynes and coworkers then extended the non-adiabatic proton transfer model [102][103][104] by incorporating a low-frequency vibrational motion between proton donor and acceptor, i.e. the Q mode, indicating that the rate constant for non-adiabatic proton transfer is the sum of k n !…”