Gas phase hydrogen bonding was studied via infrared spectroscopy in th
e 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 enth
alpies were determined. The hydrogen bond energy for all four complexe
s was within 2.0 kJ mol(-1) of -18.3 kJ mol(-1), indicating that the h
ydrogen bond energy is only minimally affected by nonlocal molecular s
tructure. The acetone-hydrogen chloride complex was modeled by ab init
io 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.