Relative and absolute bond dissociation energies of sodium cation-alcohol complexes determined using competitive collision-induced dissociation experiments

ManuscriptAbsolute (R1OH)Na+-(R2OH) and relative Na+-(ROH) bond dissociation energies are determined experimentally by competitive collision-induced dissociation of (R1OH)Na+(R2OH) complexes with xenon in a guided ion beam mass spectrometer. The alcohols examined include ethanol, 1-propanol, 2-propanol, n-butanol, iso-butanol, sec-butanol, and tert-butanol, which cover a range in Na+ affinities of only 11 kJ/mol. Dissociation cross sections for formation of Na+(R1OH) + R2OH and Na+(R2OH) + R1OH are simultaneously analyzed with a model that uses statistical theory to predict the energy dependent branching ratio. The cross section thresholds thus determined are interpreted to yield the 0 K (R1OH)Na+-(R2OH) bond dissociation energies and the relative 0K Na+-(ROH) binding affinities. The relative binding affinities are converted to absolute 0 K Na+-(ROH) binding energies by using the absolute bond energy for Na+-C2H5OH determined previously in our laboratory as an anchor value. Comparisons are made to previous experimental and theoretical Na+-(ROH) thermochemistry from several sources. The absolute (R1OH)Na+-(R2OH) bond dissociation energies were also calculated using quantum chemical theory at the MP2(full)/6-311+G(2d,2p)//MP2(full)/6-31G(d) level (corrected for zero-point energies and basis set superposition errors) and are generally in good agreement with the experimentally determined values

Experimental and Theoretical Characterization of a Lone Pair−π Complex: Water–Hexafluorobenzene

The lone pair−π interaction between H₂O and C₆F₆ was studied using matrix isolation infrared spectroscopy and quantum chemical calculations. Co-deposition of H₂O with C₆F₆ in a nitrogen matrix at 17 K followed by annealing to 30 K, results in the appearance of multiple new peaks in the infrared spectrum that are shifted from the H₂O and C₆F₆ parent absorptions. These peaks only appear when both the H₂O and C₆F₆ are present and have been assigned to distinct structures of a 1:1 H₂O·C₆F₆ complex. Similar experiments were performed with D₂O and HDO and the corresponding infrared peaks for the structures of the D₂O·C₆F₆ and HDO·C₆F₆ complexes have also been observed. Theoretical calculations were performed for the H₂O·C₆F₆ complex using the B3LYP, MP2, and CCSD­(T) methods. Geometry optimizations at the B3LYP/aug-cc-pVTZ and MP2/aug-cc-pVDZ levels of theory located three structural minima, all of which involve the lone pair−π interaction between the H₂O and the C₆F₆ ring, but with different relative orientations of the H₂O and C₆F₆ subunits. BSSE corrected interaction energies were estimated at the CCSD­(T)/aug-cc-pVTZ level and found to be between −11.2 and −12.3 kJ/mol for the three H₂O·C₆F₆ structures. Vibrational frequencies for the each of the structures were calculated at the B3LYP/aug-cc-pVTZ and MP2/aug-cc-pVDZ levels. The frequencies calculated with both methods support the assignments of the observed new peaks in the infrared spectra to the structures of the H₂O·C₆F₆ complex; however, the B3LYP calculated frequency shifts were found to be in better quantitative agreement with the experimentally observed frequency shifts