Hydrogen Bond Energies of Hydrogen Chloride−Carbonyl Complexes

Gas phase hydrogen bonding was studied via infrared spectroscopy in the following systems: methyl acetate−hydrogen chloride, methyl formate−hydrogen chloride, 2-butanone−hydrogen chloride, and acetone−hydrogen chloride. The intensity of the H−Cl stretching vibration was monitored as a function of temperature, and the hydrogen bond energies and enthalpies were determined. The hydrogen bond energy for all four complexes was within 2.0 kJ mol-1 of −18.3 kJ mol-1, indicating that the hydrogen bond energy is only minimally affected by nonlocal molecular structure. The acetone−hydrogen chloride complex was modeled by ab initio methods. The energy of formation of the complex, calculated at the MP2/6-311++G** level of theory, is −20.8 kJ mol-1, in good agreement with the experiment.