1H NMR and DFT study of proton exchange in heterogeneous structure of pyridine-N-oxide/HC1/DC1/H2O

Moderately narrow H-1 NMR signals were observed in the solid-phase obtained from pyridine-N-oxide (PyO)... HCl solutions in acetonitrile/H2O after heterogeneous phase separation. High-resolution H-1 NMR spectra are compared with those of crystalline PyO...HCl and PyO...DCl. It is concluded that partially resolved peaks in H-1 NMR spectra of solids are related with heterogeneity of the spin system and the presence of different mobile H-bond clusters containing PyO, HCl, DCl and water molecules. Some part of non-bonded water or HCl molecules is captured in the cavities of crystalline samples. The attribution of the 1 H NMR signals was based on the density functional theory calculation of proton magnetic screening tensor of the most expected H-bond structures in the 6-311G** basis taking into account the solvent effect by the polarized continuum model. (C) 2004 Elsevier B.V. All rights reserved.