By using the potentiometric titration method, standard equilibrium constants have been determined of acid dissociation of molecular acid, K-a(HA), cationic acid, K-a(BH+), of anionic and cationic homoconjugation, KAHA- and KBHB+, respectively, and of molecular heteroconjugation, K-AHB (K-BHA) in (acid + base) systems without proton transfer consisting of n-butylamine and acetic acid in binary (acetone + cyclohexane) solvent mixtures. The results have shown that both the pK(a)(HA) and pK(a)(BH+), as well as IgK(AHA-) values change non-linearly as a function of composition of the solvent mixture. On the other hand, standard molecular heteroconjugation constants without proton transfer do not depend on the cyclohexane content in the mixture, i.e. on solvent polarity. (c) 2004 Elsevier Ltd. All rights reserved.