Abstract

European Journal of Mass Spectrometry
Volume 10 Issue 6, Pages 813–818 (2004)
doi: 10.1255/ejms.699

Tetrafluorobenzyne thermochemistry: experiment and theory

Lawrence M. Pratt^*
Department of Chemistry, Fisk University, Nashville, TN 37208, USA
Alireza Fattahi and Steven R. Kass^*
Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455, USA. E-mail: kass@chem.umn.edu

Gas-phase thermodynamic properties of 1,2,3,4-tetrafluorobenzyne (1 – H₂) 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 – H₂ (ΔH°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.

Keywords: FT-MS, benzyne, thermochemistry, bond dissociation energies, radical anions, computations

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