General tendencies in structure modifications resulting from proton transfer in complexes of six selected phenols with trimethylamine are established on the basis of DFT B3LYP/6-31G(d,p) calculations with complete optimization of the structure for a given OH distance. It was found that various parameters linearly depend on C-O distance (d(CO)). Separate correlation lines are obtained for the complexes of different phenols. Values d(CO) depend on substitution and are proportional to pK(a). The O-H distance does not depend on pK(a) in free phenols, but is strongly sensitive, while is engaged into hydrogen bond. (C) 2004 Elsevier B.V. All rights reserved.