Infrared spectroscopic characterization of hydrogen-bonded propylene oxide − ethanol and propylene oxide − 2-fluoroethanol complexes isolated in solid neon matrices

The infrared absorption spectra of hydrogen-bonded complexes of propylene oxide with either ethanol or 2-fluoroethanol have been recorded in neon matrices. Mixtures of propylene oxide and ethanol or propylene oxide and 2-fluoroethanol vapors were mixed with an excess of neon gas and deposited onto a KBr substrate at 4.2 K. The results indicate that hydrogen-bonded complexes were formed with propylene oxide as the hydrogen bond acceptor and either ethanol or 2-fluoroethanol as the hydrogen bond donors. The features assigned to the O−H stretch were red-shifted by 175 and 193 cm−1 for the ethanol- and 2-fluoroethanol-containing complexes, respectively. The difference in red shifts can be accounted for due to the greater acidity of 2-fluroethanol. Deuterium isotope experiments were conducted to help confirm the assignment of the O–H stretch for the complexes. As well, structures and infrared spectra were calculated using B3LYP/6-311++G(2d,2p) calculations and were used to compare with the experimental spectra. A “scaling equation” rather than a scaling factor was used and is shown to greatly increase the utility of the calculations when comparing with experimental spectra. An examination of the O–H stretching red shifts for many hydrogen-bound complexes reveals a relationship between the shift and the difference between the acidity of the hydrogen bond donor and the basicity of the hydrogen bond acceptor (the enthalpy of proton transfer). Both hydrogen-bonded complexes and proton-bound complexes appear to have a maximum in the reduced frequency value that corresponds to complexes where the hydrogen/proton are equally shared between the two bases.

Thermodynamics of acid dissociation of aqueous bisulfite ion: ΔH0, ΔCP0, and ΔV0 at 298.15 K

Calorimetric measurements of the enthalpy of protonation of sulfite ion and the enthalpy of proton transfer from bisulfite ion to carbonate ion have led to two independent values for the standard enthalpy of the acid dissociation reaction represented by HSO3−(aq) = H+(aq) + SO32− (aq). Further calorimetric and density measurements have led to apparent and partial molar heat capacities and volumes for sulfite and bisulfite ions. Results of all of these measurements are summarized by ΔH0 = −3.59 ± 0.10 kJ mol−1, ΔCP0 = −262 ± 7 J K−1 mol−1, and ΔV0 = −28.7 ± 1.0cm3 mol−1 for the acid dissociation of HSO3− (aq) at 298.15 K. These results are used for thermodynamic calculations of the temperature and pressure dependence of the equilibrium constant for acid dissociation of HSO3− (aq).