| OCR Text |
Show to be very fragile with T99s below 650°C. Hexachlorocyclohexane has a four center concerted elimination pathway that can ultimately result in the formation of trichlorobenzene. This is also a very low energy (activation energy ~50 kcal/mole) resulting in a T99 of 640°C. The three perhalogenated methanes, dichlorodifluoromethane, trichlorofluoromethane, and carbon tetrachloride, have lowest bond dissociation energies (carbon-chlorine) of 76, 73, and 70 kcal/mole, respectively. [11] This correlates well with their experimentally determined Tggs of 790, 780, and 670, although the calculated T99S based on estimated Arrhenius parameters are about 40°C higher than the observed values. 1,1,2-trichloro-1,2,2-trifluroethanes and hexachloroethane are also expected to have weak carbon-chlorine and/or carbon-carbon bonds in the range of 75 kcal/mole and are also very fragile. The reaction path degeneracy for hexachloroethane (possible bond rupture at 6 carbon-chlorine bonds as well as the carbon-carbon bond) make it exceptionally fragile with The remaining halomethane~; chloromethane, bromomethane, and ~ . - - ' ~ dichloromethane; are all quite stable probably decomposing by hydrogen abstraction by hydroxyl radical or chlorine displacement by hydrogen atoms. The observed trend in stability is consistent • with both pathways. A complicating factor for chloromethane and bromomethane is that they may be readily reformed as PICs, which results in an apparent increase in their stability. |
