Stacked complexes made of phenol and substituted benzenes are studied via MP2 calculations in order to investigate the influence of the stacking interaction on the acidity of phenol. Aqueous-phase proton affinities have been computed and converted to pK(a) values using a calibration procedure involving a set of substituted phenols. Both T-shaped and parallel-displaced conformations lead to an appreciable decrease in the pKa, with the largest effect found for T-shaped arrangements. Local and global DFT based reactivity descriptors are used to analyze the effect of the stacking partner as well as the interaction between the aromatic rings. (c) 2005 Elsevier B.V. All rights reserved.