Abstract
The photoaddition of hydrogen bromide to tetrafluoroethylene has been studied in the gas phase using a wide variety of conditions. The rate expression is k5[HBr]z.frac32;(I0/k8)½, where k5 is the rate constant of the hydrogen-abstraction step, and k8 is the rate constant of the dimerization of 1,1,2,2-tetrafluoro-2-bromoethyl radicals. The importance of dimerization as the chain terminator and the reported exothermicities of fluorocarbon reactions are interpreted in terms of an irreversible bromine atom+tetrafluoroethylene addition. The lack of any inert gas effect suggests that the intermediate addend radicals exist in their vibrational ground states. The activation energy, determined over a temperature range 50–130°C, is +2.28 ± 0.15 kcal/mole.

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