Theoretical Study on the Gas Phase Reaction of Allyl Bromide with Hydroxyl Radical

Abstract

Mechanisms and reaction channels of the allyl bromide (CH2CHCH2Br) with OH reaction are studied using quantum chemistry. It is predicted that the H(or Br)-abstraction and addition/elimination mechanisms have been revealed on potential energy surface (PES). Direct H-abstract from the CH2Br group of CH2CHCH2Br leading to h-P1 (CH2CHCHBr+H2O) is dominant. As for addition/elimination mechanism, it is shown that the reaction is initiated by the addition of OH radical to the CC bond of CH2CHCH2Br to barrierlessly generate the intermediates IM1 and IM2, respectively. Multichannel RRKM theory and variational transition-state theory (VTST) are employed to evaluate the rate constants of temperature- and pressure-dependent. The calculated rate constants are in good agreement with the available experimental data. At 100Torr with helium as bath gas, IM3 (CH2OHCHBrCH2) formed by collisional stabilization and the final products P1 (CH2OH+CH2CHBr) are the major product in the temperature range of 200–700K and 700–1000K, respectively. The production of CH2CHCHBr via hydrogen abstraction becomes dominant at high temperatures (T⩾1000K). Time-dependent DFT (TD-DFT) calculations indicate that IM1-IM4, IM6, IM8 and IM9 take photolysis easily in the sunlight at the wavelength of 333nm, 244nm, 327nm, 313nm, 298nm, 305nm and 428nm, once they are generated.