Infrared spectroscopic studies of hydrogen bonding in triethylammonium salts. Part 2.—Association of triethylammonium salts with bases

Abstract

Parameters of the i.r. ν_N⁺H stretching mode bands of triethylammonium perchlorate, fluoroborate and iodide dissolved in pure (base B) and binary (B + chloroform) solvents have been measured. A dynamic equilibrium Et₃N⁺H⋯A^–+ B ⇌[Et₃N⁺H⋯B]A^– is shown to exist in the solutions. Association constants K_a and enthalpies –ΔH of this process have been determined by measuring the total areas of the i.r. absorption ν_N⁺H bands in both hydrogen-bonded complexes. The dependence of K_a values on the strength of the base B and its dipole moment is discussed. Electrostatic interactions are shown not to contribute to the enthalpy of transition from the ionic pair Et₃N⁺H ⋯ A^– to the ion-molecular complex Et₃N⁺H ⋯ B, the latter forming a contact pair with the anion A^–. The results do not reveal any differences in the spectral manifestations of hydrogen bonding in intermolecular, ion-molecular complexes and ionic pairs.