Tetrafluorobenzyne thermochemistry: experiment and theory

摘要

Gas-phase thermodynamic properties of 1,2,3,4-tetrafluorobenzyne (1-H-2) were determined by Fourier transform mass spectrometry and ab initio and density functional theory methods. 1,2,3,4-Tetrafluorobenzyne radical anion was generated by abstraction of a proton and a hydrogen atom upon reaction of 1,2,3,4-tetrafluorobenzene (1) with O-.. The resulting structure was confirmed by converting it to a species which could be independently prepared. Bracketing results provided the proton affinity of 1,2,3,4-tetrafluorobenzyne radical anion and the electron affinities of 1,2,3,4-tetrafluorobenzyne and 1,2,3,4-tetrafluorophenyl radical. These measured values were combined in a thermodynamic cycle to provide the heat of hydrogenation of 1-H-2 (Delta H degrees(hyd) = 367 +/- 18 kJ mol(-1)) and the first and second C-H bond dissociation energies of 1 (481 +/- 11 and 321 13 kJ mol-1). The same approach failed for the meta and para isomers, but their energetics were examined using B3LYP and CCSD(T) computations.