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Ring Expansion Reactions in the Thermal Decomposition of t-Butyl-1,3-Cyclopentadiene



William S. McGivern, Jeffrey A. Manion, Wing Tsang


The thermal decomposition of t-butyl-1,3-cyclopentadiene has been investigated in single pulse shock tube studies at shock pressures of 182 260 kPa and temperatures of 996 1127 K. Isobutene (2-methylpropene), 1,3-cyclopentadiene, and toluene are observed as the major stable products in the thermolysis of dilute mixtures of the substrate in the presence of a free radical scavenger. Hydrogen atoms were also inferred to be a primary product of the decomposition and could be quantitatively determined on the basis of products derived from the free radical scavenger. Of particular interest is the formation of toluene, which involves the expansion of the ring from a five to a six-membered system. The overall reaction mechanism is suggested to include isomerization of the starting material, a molecular elimination channel, and C C bond fission reactions, with toluene formation occurring via radical intermediates formed in the latter pathway. These radical intermediates are analogous to those believed to be important in soot formation reactions occurring during combustion. Molecular and thermodynamic properties of key species have been calculated from G3MP2B3 quantum chemistry calculations and are reported. The temperature dependence of the product spectrum has been fit with a detailed chemical kinetic model and best-fit kinetic parameters have been derived using a Nelder-Mead simplex minimization algorithm. Our mechanism and rate constants are consistent with and provide experimental support for the H-atom assisted routes to the conversion of fulvene to benzene that have been proposed in the literature on the basis of theoretical investigations.
Journal of Physical Chemistry A


benzene, fulvene, kinetics, ring expansion, shock tube, soot formation, t-butyl-1, 3-cyclopentadiene


McGivern, W. , Manion, J. and Tsang, W. (2006), Ring Expansion Reactions in the Thermal Decomposition of t-Butyl-1,3-Cyclopentadiene, Journal of Physical Chemistry A, [online], (Accessed June 25, 2024)


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Created November 30, 2006, Updated November 18, 2016