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A Shock Tube Study of H Addition to Cyclopentene



Jeffrey A. Manion, Iftikhar A. Awan


The kinetics of H atom addition to cyclopentene has been studied with a single pulse shock tube at temperatures of (863 to 1167 K) and pressures of (160 to 370) kPa. Hydrogen atoms were generated with thermal precursors in dilute mixtures of cyclopentene in argon. Addition of H to the double bond leads to a cyclopentyl radical that rapidly ring opens and decomposes to ethene and allyl radical. The overall process was monitored by post-shock gas chromatographic analysis of ethene. Kinetic parameters have been determined relative to a reference reaction, the displacement by H of methyl from 1,3,5-trimethylbenzene (135TMB). At (863 to 1167) K and (160 to 370) kPa we find: k(H+cyclopentene → ethene+allyl)/k(H+135TMB → m-xylene+CH3) = 10-0.244 exp(1819 K/T), and, with k(H+135TMB → m-xylene+methyl) = 6.76 x 1013exp(-3255 K/T ) cm3mol-1s-1, we obtain: k(H + cyclopentene → ethylene + allyl) = 4.79 x 1013 exp(-1435 K/T) cm3mol-1s-1 Using experimental branching ratios in the decomposition of cyclopentyl radicals and a corresponding RRKM model (I.A. Awan, D.R. Burgess, Jr. W. Tsang, J.A. Manion, Proc. Combust. Inst. 33 (2011) 341–349), the high pressure limiting rate expression for addition of H atom to cyclopentene at (863 to 1167) K has been derived as k∞(H+cyclopentene → cyclopentyl) = 6.04 x 1013 exp(-1391 K/T) cm3mol-1s-1 Combined with literature results from lower temperatures and a fitted transition state theory model the rate expression between 298 K and 2000 K is determined as: k∞(H+cyclopentene → cyclopentyl) = 1.37×108 𝑇1.729 exp(−372 K⁄𝑇) cm3 mol−1s−1; Results are compared with related systems and some incompatibilities with existing kinetics models of cyclopentane combustion are noted. We additionally report and discuss minor observed channels in the decomposition of cyclopentene, including formation of 1,4-pentadiene, (E/Z)-1,3- pentadiene, 1,3-butadiene, and the direct elimination of H2 from cyclopentene to give cyclopentadiene.
Journal of Physical Chemistry A


kinetics, hydrogen atoms, cyclopentyl, 1, 4-pentadiene, 1, 3-pentadiene, 1, 3-butadiene.
Created February 1, 2018, Updated September 21, 2018