In a recent experimental study of proton transfer in benzoic acid, employing field cycling NMR relaxometry (Chem. Phys. Lett. 402 (2005) 519), the authors came to the conclusion that the transition between the quantum and classical regimes is smooth and that the spectral densities of proton transfer are characterised by a single correlation time. The analysis presented, however, of the same field cycling NMR relaxometry data in terms of Schrodinger's equation shows that the proton transfer dynamics is characterised by two correlation times tau(ov) (Arrhenius) and tau(tu) (Schrodinger), which characterise two fundamentally different motional processes, namely jumps over the barrier and tunnelling through the barrier. The temperature dependence of the (1/tau(tu)) is the solution of Schrodinger's equation, which also yields the temperature T-tun, where begins the tunnel pathway for proton transfer. Below Ttun the energy of the particle is lower than the value of the potential barrier that the particle has to pass over. Above T-tun the length of the de Broglie wave generated by thermal motion is too short to pass through the potential barrier. (c) 2006 Elsevier B.V. All rights reserved.