The cis-trans isomerization of chemically activated 1-methylallyl is investigated using RRKM/Master Equation methods for a range of pressures and temperatures. This system is a prototype for a large range of allylic radicals formed from highly exothermic (∼35 kcal/mol) OH + alkene reactions. Energies, vibrational frequencies, anharmonic constants, and the torsional potential of the methyl group are computed with density functional theory for both isomers and the transition state connecting them. Chemically activated radicals are found to undergo rapid cis-trans isomerization leading to stabilization of significant amounts of both isomers. In addition, the thermal rate constant for trans → cis isomerization of 1-methylallyl is computed to be high enough to dominate reaction with O(2) in 10 atm of air at 700 K, so models of the chemistry of the (more abundant and more commonly studied) trans-alkenes may need to be modified to include the cis isomers of the corresponding allylic radicals. Addition of molecular oxygen to 1-methylallyl radical can form 2-butene-1-peroxy radical (CH(3)CH═CHCH(2)OO(•)), and quantum chemistry is used to thoroughly explore the possible unimolecular reactions of the cis and trans isomers of this radical. The cis isomer of the 2-butene-1-peroxy radical has the lowest barrier (via 1,6 H-shift) to further reaction, but this barrier appears to be too high to compete with loss of O(2).

Propane is the smallest molecule that can serve as a model of the chemistry of diesel autoignition. Diesel autoignition requires H-migration reactions of the type •OOCH 2 CH 2 CH 2 OOH → HOOCH 2 CH 2 C•HOOH. Previous studies of this type of H-migration reactions accounted for tunneling (through-barrier processes) using 1-D models of the reaction coordinate, namely, the Eckart or Wigner approximations. Here we present the first study to use multi-dimensional approaches, specifically, small-and large-curvature tunneling, to treat through-barrier processes. Calculations are carried out using the POLYRATE program and make use of the M05-2X/6-31+G(d,p) level of theory.