The 1,2-Interchange of F and Cl interconverting CH2FCD2Cl and CH2ClCD2F

Abstract

CH₂FCD₂Cl was prepared using gas-phase recombination of CH₂F and CD₂Cl radicals, at 25°C with an internal energy of 91 kcal mol-1. Three unimolecular processes compete with collisional deactivation: HCl and DF elimination to give CHF=CD₂ and CH₂=CDCl and isomerization of CH₂FCD₂Cl to give CH₂ClCD₂F by means of halogen interchange. The formation of CHCl=CD₂, via HF elimination from CH₂ClCD₂F, was observed and a rate constant was assigned for the interchange reaction. Previous publications on chemically activated CH₂ClCH₂F, along with this current study allow the designation of the three unimolecular rate constants. The halogen rearrangement has a branching ratio of 0.25 ± 0.05. When compared, the experimental rate constant along with the rate constant calculated using Rice Rasmburger Kassel Marcus (RRKM) theory produces a threshold energy of 59 ± 2 kcal mol-1 for this type 1 dyotropic rearrangement. All three unimolecular processes have similar threshold energies. CD₂ClCD₂Cl and CH₂FCH₂F molecules are also generated from the radical recombination reactions, and the rate constants for DCl and HF elimination were measured in order to confirm that reliable data for CH₂FCD₂Cl was obtained from the photolysis of CD₂ClI and (CH₂F)₂CO.