Résumé : U.V. studies of hydrogen bonding between monoaza-aromatic compounds (pyridine quinoline, acridine⋯) and a series of carboxylic acids in hexane solution, confirm the existence of a tautomeric equilibrium involving the associated base and the protonated base. The fraction of both species are estimated in every case. Solvent effects on the structure of the complex of quinoline, isoquinoline and acridine with acetic acid are discussed. Our experimental results agree with a double well potential for this type of hydrogen bonds. © 1963.