By using the potentiometric method the following quantities have been determined: acidity constants of molecular acid, K-a(HA), of cationic acid, K-a(BH+), anionic and cationic homoconjugation constants, KAHA-and KBHB+, respectively, as well as molecular heteroconjugation constants, K-AHB, in (n-butylamine + acetic acid) systems without proton transfer in binary (acetonitrile + 1,4-dioxane), AN + D, solvent mixtures. The results of these measurements have shown that the magnitudes of the molecular heteroconjugation constants do not depend on the 1,4-dioxane content in the mixed solvent, i.e., on solvent polarity. It has also been found that in the (acid + base) systems without proton transfer, the manner of carrying out the titration (direct B + HA vs. reverse HA + B) does not affect the magnitudes of the molecular heteroconjugation constants. (C) 2005 Elsevier Ltd. All rights reserved.