(Acid + base) equilibria, including molecular heteroconjugation ones, between n-butylamine and one of the following phenols: 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol, 2,5-dinitrophenol, 3-chlorophenol, 4-chlorophenol, 2,3,4,5,6-penta-chlorophenol and 2,4,6-tribromophenol have been studied potentiometrically in a protophobic polar aprotic solvent, acetonitrile. Among the phenols studied, 2,5-dinitrophenol exhibited the strongest tendency towards formation of asymmetric hydrogen bonds with n-butylamine, whereas a weakest complex was formed with 2-nitrophenol. In the (n-butylamine + 2,3,4,5,6-pentachlorophenol) and (n-butylamine + 2,4-dinitrophenol) systems proton transfer reactions occurred. (c) 2004 Elsevier Ltd. All rights reserved.