Thermochemical Evidence of OH–π Type Intermolecular Hydrogen Bonds

Abstract

Abstract A calorimeter for measuring the heat of mixing was constructed. Using the calorimeter, the heats of mixing were measured at 25.0±0.01°C for binary mixtures of benzyl alcohol with ethyl benzene or cyclohexane and ethyl benzene with cyclohexane, and at 35.0±0.01°C for binary mixtures of m-cresol with m-xylene or cyclohexane and m-xylene with cyclohexane. By plotting the values of the heats of mixing, ΔHx1M against the mole fraction of component 1, x1 and by extrapolating the curve to an infinite dilution (x1→0) for each system, the heats of mixing at an infinite dilution (\undersetx1→0limΔHx1M) were obtained graphically. By using the values of \undersetx1→0limΔHx1M obtained for these systems and by applying an enthalpy cycle, the OH–π type intermolecular hydrogen bond energies were estimated to be ΔH=−6.2 kJ for the benzyl alcohol-ethyl benzene - cyclohexane system and ΔH=−13.1 kJ for the m-cresol - m-xylene - cyclohexane system. The results obtained have been discussed from two points of view, that is, the proton-donating power of alcohols and the proton-accepting power of aromatic hydrocarbons.