Carbon-hydrogen bonds tunneling

In this case the parameters C and Q are of order of unity, and therefore they correspond to the intermediate situation between the sudden and adiabatic tunneling regimes. Examples are mal-onaldehyde, tropolon and its derivatives, and the hydrogen-oxalate anion discussed above. For intermolecular transfer, corresponding to a weak hydrogen bond, the parameters C, Q and b are typically much smaller than unity, and the sudden approximation is valid. In particular, carbonic acids fulfill this condition, as was illustrated by Makri and Miller [1989]. 

Ionic dissociation of carbon-carbon a-bonds in hydrocarbons and the formation of authentic hydrocarbon salts, 30, 173 Ionization potentials, 4, 31 Ion-pairing effects in carbanion reactions, 15, 153 Ions, organic, charge density-NMR chemical shift correlations, 11, 125 Isomerization, permutational, of pentavalent phosphorus compounds, 9, 25 Isotope effects and quantum tunneling in enzyme-catalyzed hydrogen transfer. 

Figure 8.9 INS spectrum of KHCOj at 4 K in the tunnelling region and band decomposition into Gaussian profiles. Reproduced with permission from Chem. Phys. 124, F. Fillaux, J. Tomkinson and J. Penfold, Chem. Phys., Proton Dynamics in the Hydrogen Bond. The Inelastic Neutron Scattering Spectrum of Potassium Hydrogen Carbonate at 5K, 425, Copyright (1988) Elsevier.

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