Self-Association of some organic acids in aqueous solutions

The self-association of both phenyl acetic acid [PAA] and hydrocinnamic acid [HCA] in aqueous solutions has been studied at 25 degree. Vapor pressure osmometry was used to count the number of particles presented in dilute aqueous solutions of non-volatile compounds. The data obtained were best fitted by assuming the formation of 1: 1 dimers. The association is most likely to occur through stacking of the phenyl groups with the side chain oriented on the opposite sides of the stacked pair. The dimerization equilibrium constants have been computed for both acids. From the results, it is possible to discuss the effect of the side chain length on the dimerization constant