Abstract
Bond strengths. The heat of formation of CF2 has been estimated through electron impact, thermochemical and kinetic studies. The most recent measurements were obtained through a study of the pyrolysis of CF2HC1 at 530°–750° C, which is believed1–3 to follow the mechanism: 
Either by interpolation from known data, or by assuming the heat of formation of C2F4 (−151.5 kcal/mole (ref. 4) ) and combining this with the thermodynamic data for the equilibrium: 
it is possible to estimate the heat of formation of CF2HC1 (∼ − 112 kcal/mole); an estimate of the Arrhenius factors of the elementary steps can be derived from the kinetic analysis. Combination of the thermochemical and kinetic data yields ΔHf(CF2) ≲ − 40 kcal/mole, and hence D(F2C−CF2) ≲ 70 kcal/mole. Similar conclusions have been reached by Stull5, on the basis of a study of the formation of C2F4 from carbon and CF4 in a furnace6. Majer and Patrick7 have suggested that higher (less negative) values for ΔHf(CF2), which have been reported on the basis of electron impact studies, result from the production of excited fragments in the primary dissociation.
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SIMONS, J. Chemical Behaviour of Difluorocarbene, and the Dissociation of the Carbon—Carbon Bond in Tetra-fluoroethylene. Nature 205, 1308–1309 (1965). https://doi.org/10.1038/2051308a0
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DOI: https://doi.org/10.1038/2051308a0
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