The basicity of aniline derivatives substituted with F, Cl, OH, NO2, and CN groups in ortho, meta, and para positions is quantitatively related to different properties obtained from the QTAIM theory. The linear relationships obtained between these properties and the pK(a) values improve significantly when ortho, meta, and para substituted anilines are considered independently. In particular, the worst correlations are obtained for the ortho substituted derivatives and the better results for the para substituted derivatives. (c) 2005 Elsevier B.V. All rights reserved.