A mechanism is proposed of intramolecular reorganization leading to equalization of the energies of reactants and products in a nonequilibrium proton transfer reaction. The model proposed allows one to extend a conventional quantum chemical treatment to gas phase proton transfer. Taking the reaction of toluene deprotonation with the CH 2 CN -anion (a conjugate base of acetonitrile) as an example, it was shown that the activation energy and its components can be determined from direct ab initio calculations. The effect of disbalance of structural changes relative to the "equilibrium" proton transfer is considered.Reorganization of systems in the course of chemical reactions is a key problem in the kinetic and reactivity studies. Quantum theories of charge transfer in solution 1,2 usually treat the reorganization of a system as changes in the configuration of heavy nuclei of reactants and their solvation shell, which precede transfer of a light particle (electron or proton). Correspondingly, intra and inter molecular reorganization are distinguished. For instance, the reorganization energy of a thermally neutral reaction λ appeared in the Marcus equation 1 (Eqs (1a-d)) is de fined as the sum of the internal (λ i ) and external (λ ο ) con tributions.where ΔG** and ΔG 00 are the Gibbs free energy of activa tion and reaction, respectively; ΔG* and ΔG 0 are the corre sponding parameters for proton transfer in the encounter complex; and w r and w p characterize the changes in the energy of the system upon formation of the encounter com plex from the reactants and products, respectively. In the case of proton transfer reactions, the appearance of the parameter λ in Eqs (1a)-(1d) is associated with the generalized Frank-Condon principle, 3 which postulates no changes in the coordinates and velocities of heavy nu clei during proton transfer. Based on the condition for conservation of the energy of the system at the instant of transfer, transformations of the system in the state of an encounter complex are schematically described as a three step process including successive motion of the represen tation point of the system along the classical (reorganiza tion) coordinate q and the quantum (proton) coordinate r. The coordinate q corresponds to the rise of the system along the reactant term (first step) and to the descent along the product term (third step) (Fig. 1, a). Transition of the system from the initial to the final term (second step) is treated as the motion along the coordinate r, which is due to the proton jump at a fixed q = q* (intersection point of two terms). In the nonadiabatic limit, transfer of a proton in the activated complex (AC) occurs by tunneling in a symmetric two well potential (Fig. 1, b). In this case the activation (Frank-Condon) barrier appears as a result of the overall mismatch between the configurations of the classical (heavy nuclei) and quantum (electrons and pro ton) subsystems at the instant of proton transfer. The pa rameter λ playing the role of a criterion for this mismatch and the Gibb...

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