A theoretical and experimental N-14 NMR study of association of pyridine

The N-14 NMR spectra of liquid pyridine and its mixtures with n-heptane wer e measured over a full concentration range. The chemical shifts of the pyri dine nitrogen were found to vary in the spectra of the mixtures as compared with the value for the pure base. These variations were compared with theo retical results, i.e. with the difference in shielding constant for the nit rogen nucleus in the isolated molecule and its associates (calculated by GI AO/CHF). The geometry of pyridine molecules and of its associates was optim ised at RHF/6-31 +G** level. On this basis the most probable structures for the associates in liquid pyridine were proposed. The computer simulation o f liquid pyridine at a temperature of 300 K, by the molecular dynamics meth od using the Amber force field, lent validity to the existence of the propo sed dimers. (C) 2001 Published by Elsevier Science B.V.