Multiple Hydrogen Transfer in H-bonds of Medium Strength

6 Intermolecular Multiple Hydrogen Transfer in H-bonds of Medium Strength 

The double proton transfer in cyclic dimers of crystalline benzoic acid has been studied by various authors using NMR relaxation techniques [72, 73]. For a recent account of this work the reader is referred to the study of Horsewill et al. [74] who published the correlation times of the HH, HD and DD reactions given by 

A represents the energy difference between the two tautomers whose gas-phase degeneracy is lifted by solid-state interactions. Xj and %2 represent the mole-fractions. 

The tautomerism of crystalline pyrazoles which is discussed in the following, is particularly interesting because of the variety of hydrogen bonded complexes 

The Arrhenius diagram of the degenerate HH/HD/DD transfer in the cyclic dimer of crystalline 3,5-diphenyl-4-bromopyrazole (DPBrP) [27] is depicted in Fig. 

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