The bond dissociation energies in F3
- are determined from energy-resolved collision-induced
dissociation cross sections measurements in two tandem mass spectrometers. The gas-phase F2−F- bond
dissociation energy is measured to be 1.02 ± 0.11 eV, and the energy for dissociation to F + F2
- is 0.28 ±
0.07 eV higher. After accounting for solvation energies, it is shown that the F3
- is not expected to be stable
with respect to dissociation in aqueous solution. Last, from the spectroscopic parameters, it is deduced that
F2
- formation is favored at high energies, in agreement with experimental results.
A flowing afterglow−tandem mass spectrometer has been used to determine 0 K bond strengths in three
hypervalent polyhalide ions: D(Cl2−Cl-) = 99 ± 5 kJ/mol, D(Br2−Br-) = 127 ± 7 kJ/mol, and D(Br2−Br3
-) = 40 ± 7 kJ/mol. These bond strengths are close to the previously measured values D(I2−I-) = 126
± 6 kJ/mol and D(I2−I3
-) = 49 ± 6 kJ/mol. In contrast, Cl5
- and F3
- are not formed at room temperature
in the flowing afterglow. Solvation energies for the trihalides derived from this work and literature
thermochemistry are inversely correlated with the size of the ion, in reasonable agreement with the predictions
of the Born model. The electron affinities EA(Cl3) = 4.60 ± 0.09 eV and EA(Br3) = 4.55 ± 0.10 eV can
also be derived. The gas-phase bond strengths are more consistent with the three center-four electron bond
model than with the expanded octet model.
A combined computational and experimental study on the gas-phase structures and reactivities of charged 1,3-didehydroarenes (meta-benzynes) demonstrates that the reactivity of such biradicals can be "tuned" by using appropriate substituents. Substituents that destabilize a specific zwitterionic resonance structure can change the reactivity of the biradical from mildly carbocationic to radical-like. These substituent effects are not the result of changes in the singlet-triplet gaps of the biradicals, but rather reflect changes in the potential energy surfaces for the dehydrocarbon separation.
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