Infrared spectroscopic investigations of acid–base interactions in aprotic solvents. Part I. The interaction of tri-n-propylamine and some carboxylic acids

Abstract

The infrared absorption spectra of carbon tetrachloride and chloroform solutions of seven monocarboxylic acids to which various proportions of tri-n-propylamine had been added have been recorded. The results indicate a stepwise formation of 2 : 1 and 1 : 1 compounds between acid and base, the nature of the products and the extents of their formation depending on the strength of the acid and the nature of the solvent. The 1 : 1 complexes of the strongest acids appear to have ion-pair structures with symmetrical carboxylate groups, but in those of the weaker acids there seems to be a more specific interaction of the proton of the tri-n-propylammonium ion and one of the carboxylate oxygen atoms. The spectra of all the compounds containing these specific hydrogen bonds include a band near 1900 cm.^–1, the origin of which is discussed. Condensed-phase spectra have also been recorded for comparison purposes.