Dynamics of Hydrogen Transfer in Liquids and Solids

Double proton transfer in crystals of 1,3,4,6,7,8‐hexahydro‐2H‐pyrimido[1,2‐a] pyrimidine (hppH):13C and15N CPMAS NMR study of (hppH)2

“…Double proton transfer was observed by Ernst in 1990 in dimers of benzoic acids, and has been the subject of several studies since that time 1–6. Prior to these observations, a triple proton transfer was reported for 3,5‐dimethylpyrazole trimer7 that was subsequently extended to double and quadruple proton transfers in other pyrazole cyclamers,8–11 as well as to 1,2,4‐triazoles 12. Other examples were found by Limbach et al involving amidines13, 14 and triazenes 15–17.…”

“…It is possible to distinguish between these two situations using X‐ray crystallography, by determining the structure at different temperatures and analysing the anisotropic displacement parameters (ADP) 41–43. However, for fast processes (Δ G ‡ < 45 kJ mol −1 ) an alternative method that has been successfully used for distinguishing these different processes is solid‐state NMR 8–18, 44, 45. We wish to report herein a study of the behaviour of 1 2 and related bicyclic guanidines (Scheme ) in the solid state, using a combined 13 C and 15 N NMR spectroscopic and theoretical approach.…”

15N NMR Spectroscopy in Structural Analysis: An Update (2001 - 2005)

“…He considers the dependence of the results on the quantum chemical method used, on the basis set superposition error (BSSE), and the effect of the basepair geometry with varying hydrogen bond length on the relaxation. Variable-temperature high-resolution 15 N CP/MAS NMR is a highly versatile method for following the transfer of protons and deuterons to and from nitrogen in the solid state [348]. Fig.…”