SUBSTITUENT AND PH EFFECTS ON SELF-ASSOCIATION OF PYRIDINE-DERIVATIVES IN AQUEOUS-SOLUTION - AN ULTRAVIOLET STUDY

Self-association of pyridine, 2-picoline, pyridine monocarboxylic acids, methyl nicotinate, and dipicolinic acid, has been studied in aqueous solution by ultraviolet spectroscopy, as an extension of previous work. The spectra of these compounds, under suitable conditions of pH, show an hypochromic effect with increasing concentration over the range from 10(-6) to 10(-1) M, which is interpreted in terms of self-association. Association constants are calculated from dimerization and polymerization models. The results are discussed in terms of the nature of substituents and the protonation states, and show that interactions in dilute solutions are important in the self-association processes of these compounds in aqueous solution.