Proton transfer, hydrogen bonds tunneling

The availability of the coherent proton tunneling and cooperative proton tunneling and transfer of four protons in hydrogen bonds of benzoic acids crystals (including dye doped) have been revealed by Trommsdorff and collaborators [12,13] by reading the electron spectra of the crystals. 

J. M. Lopez, F. Mannle, I. Wawer, G. Buntkowsky, and H. H. Limbach, NMR studies of double proton transfer in hydrogen bonded cyclic N,N diarylformamidine dimers Conformational control, kinetic HH/HD/DD isotope effects and tunneling. Phys. Chem. Chem. Phys. 9, 4498 4513 (2007). 

The half-life of a base hydrogen-bonded to a strong acid can be very short indeed since proton transfer can occur by tunnelling thus the rate coefficient for proton transfer to water hydrogen-bonded to H30+ has been estimated at 1014 s-1 (Crooks, 1977). For the nitrations in concentrated sulphuric acid as solvent, H2S04 and HSO should take the place of H30+ and H20 in (34) (cf. Cox, 1974). 

Horsewill et al. (1994) examined the hydrostatic pressure effect on the proton transfer in crystals of a carboxylic acid dimer. Under a hydrostatic pressure, the distance of hydrogen bonds becomes shorter, and this is accompanied by a decrease in the potential barrier to proton transfer. The temperature dependence of the rate of the proton transfer turns out to be of a non-Arrhenius type. The influence of phonon-assisted tunnelling becomes evident as the external pressure increases, especially at lower temperatures. 

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