Energy disposal in the three-centered elimination of df from 1,1,2-trifluoroethane-1-d1

The chemical activation data for three- and four-centered hydrogen fluoride elimination from CH₂FCDF₂ have been analyzed to assign the energy released to the olefin fragment in the three-centered process and to estimate the threshold energies for elimination channels. Based upon the cis–trans isomerization rates of CHF = CHF, 78% of the total available energy was released to the olefin fragment for the αα channel. The analysis suggests the existence of an appreciable barrier (～10 kcal/mole) for the reverse reaction, addition of the CH₂FCF carbene to DF. The threshold energies for αα, αβ, and βα elimination from 1,1,2-trifluoroethane-1-d₁ were assigned as 71, 68, and 68 kcal/mole, respectively. Analysis of the chemical activation data for 1,1,2,2,-tetrafluoroethane, without distinguishing between the three- and four-centered elimination channels, suggests a threshold energy of ～75 kcal/mole.