Molecular heteroconjugation constants, K-BHA(DMSO) and K-AHB(DMSO) expressed as their logarithms, have been determined by potentiometric titration for eleven substituted phenol + n-butylamine systems in a polar protophilic aprotic solvent, dimethyl sulfoxide (DMSO). An increasing tendency towards molecular heteroconjugation in these systems without proton transfer has been found with increasing pK(a)(DMSO) (HA), i.e., with decreasing phenol acidity. Moreover, a linear correlation has been established between the determined a Ig K-BHA(DMSO) values and pK(a)(DMSO) (HA). Furthermore, overall stability constants, Ig K-o(DMSO), could be correlated linearly with pK(a)(DMSO) (HA) values. (c) 2004 Elsevier Ltd. All rights reserved.