Theoretical aspects of tunneling proton transfer reactions in a polar environment

This paper reviews some nontraditional theoretical views developed in this group on acid–base proton transfer (PT) reactions in hydrogen (H‐) bonded systems, focusing on the tunneling regime. Key ingredients in this picture are a completely quantum character for the proton motion (even when tunneling does not occur), the identification of a solvent coordinate as the reaction coordinate, and attention to the H‐bond vibrational ‘promoting’ mode in the acid–base complex. Attention is also given to the electronic structure rearrangements associated with PT in the electronically adiabatic regime. A general overview is presented for the tunneling rate constants including the activation free energy and the associated primary kinetic isotope effects (KIEs) for proton tunneling reactions.