Thermodynamic study of the deuterium isotope effect in hydrogen-bonded systems

Abstract

Molar excess enthalpies are reported for the systems (C₂H₅)₃N + CDCl₃, (C₂H₅)₂O + CDCl₃ and (C₂H₅)₂O + CHCl₃ at 298.15 K. Vapour pressures are reported for the system (C₂H₅)₃N + CDCl₃ at 283.15 K. The results are analysed in terms of the ideal associated solution model and the equilibrium constants and standard enthalpies of complex formation obtained are compared with spectroscopic values. Difference between the thermodynamic properties of corresponding CDCl₃ and CHCl₃ systems are discussed in terms of differences between the equilibrium constants and standard enthalpies of formation of the deuterium-bond and hydrogen-bond complexes. An analysis of calorimetric results at 298.15 K suggests that the equilibrium constant is smaller for the (C₂H₅)₃N—CDCl₃ complex than for the (C₂H₅)₃N—CHCl₃ complex, but that the magnitude of the standard enthalpy of formation is greater for the (C₂H₅)₃N—CDCl₃ complex.