Gas-phase pyrolysis mechanism and kinetics of 3-chloroquadricyclane

The gas-phase pyrolysis of 3-chloroquadricyclane [1] was investigated over the temperature range 513-550 K at one atm in helium. The initial pyrolysis step is the isomerization of 3-chloroquadricyclane to 7-chloronorbornadiene (E-a = 39.67 +/- 1.40 kcal/mole, log A = 15.18 +/- 0.58). 7-chloronorbornadiene rearranges (623-660 K) to exclusively produce benzyl chloride (E-a = 48.05 +/- 1.10 kcal/mole, log A = 15.82 +/- 0.38). This two step mechanism affords fewer reactions than the unsubstituted quadricyclane system in the gas phase. The production of a benzene derivative from the chlorinated norbornadiene is a reaction pathway contained in the unsubstituted norbornadiene and other 7-substituted pyrolysis mechanisms. (C) 1997 John Wiley & Sons, Inc.