The chemical activation data for three-and four-centered hydrogen fluoride elimination from CHtFCDFZ 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 cra channel. The analysis suggests the existence of an appreciable barrier (-10 kcal/mole) for the reverse reaction, addition of the CHZFCF carbene to DF. The threshold energies for aa, a@, and @a elimination from 1, I ,2-trifluoroethane-1 -dl 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 kcai/mole.