Conformational Effects on Gas-Phase Acidities of Isomeric C and C Alkanols.

The competitive threshold collision-induced dissociation technique is used to examine conformational effects on the relative gas-phase acidities of selected alcohols. By use of HF and HO as reference acids in a local thermochemical network to obtain absolute acidities, the measured 0 K gas-phase acidities for the propanol and pentanol isomers are Δ H(CHCHCHO-H) = 1563.9 ± 2.

Anchoring the Gas-Phase Acidity Scale from Hydrogen Sulfide to Pyrrole. Experimental Bond Dissociation Energies of Nitromethane, Ethanethiol, and Cyclopentadiene.

A meta-analysis of experimental information from a variety of sources is combined with statistical thermodynamics calculations to refine the gas-phase acidity scale from hydrogen sulfide to pyrrole. The absolute acidities of hydrogen sulfide, methanethiol, and pyrrole are evaluated from literature R-H bond energies and radical electron affinities to anchor the scale. Relative acidities from proton-transfer equilibrium experiments are used in a local thermochemical network optimized by least-squares analysis to obtain absolute acidities of 14 additional acids in the region.

Energy-resolved collision-induced dissociation of peroxyformate anion: enthalpies of formation of peroxyformic acid and peroxyformyl radical.

We measure the oxygen-oxygen bond dissociation energy of the peroxyformate anion (HCO(3)(-)) using energy-resolved collision-induced dissociation with a guided ion beam tandem mass spectrometer. The analysis of the dissociation process from HCO(3)(-) ((1)A') to HCO(2)(-) ((1)A(2)) + O((3)P) requires consideration of the singlet-triplet crossing along the reaction path and of the competing OH(-) and O(2)H(-) product channels. The measured oxygen-oxygen bond dissociation energy is D(0)(HCO(2)(-)-O) = 1.