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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Decomposition of #beta#-Hydroxypropoxy Radicals in the OH-Initiated Oxidation of Propene. A Theoretical and Experimental Study
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Decomposition of #beta#-Hydroxypropoxy Radicals in the OH-Initiated Oxidation of Propene. A Theoretical and Experimental Study

机译：OH引发的丙烯氧化反应中＃beta＃-羟基丙氧基自由基的分解。理论和实验研究

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Environmental chamber studies of the OH-initiated oxidation of propene have been carried out in the presence of nitrogen oxides under conditions relevant to the atmosphere. The major products observed at all temperatures studied (220-300 K) are CH_2O and CH_3CHO, indicating that the #beta#-hydroxypropoxy radicals formed in the oxidation process (from reaction of the corresponding #beta#-hydroxypropylperoxy radicals with NO) predominantly undergo unimolecular decomposition. A full theoretical study of the chemistry of the dominant #beta#-hydroxypropylperoxy, #beta#-hydroxypropylperoxynitrite, and #beta#-hydroxypropoxy species has been carried out. On the basis of B3L YP-DFT/6-31G~(**) quantum chemical characterizations, the most stable conformations of the oxy radicals are found to contain intramolecular hydrogen bonds, which provide stabilizations of about 2 kcal/mol. The internal hydrogen bond in the lowest-energy oxy species is found to persist in the transition states for C-C bond rupture, which keeps the barrier to their decomposition down to 7.2 kcal/mol. By use of SSE theory, the internal energy distribution of the nascent HOCH_2CH(O)CH_3 oxy radicals has been determined; it is found that most radicals are born with internal energies well above the calculated barrier for their decomposition. Thus, as determined by master equation analysis, the majority of these oxy radicals (80% at 300 K and 1 atm, 75% at 220 K and 0.2 atm) will decompose promptly before collisional stabilization, yielding CH_2OH and CH_3CHO, while the remainder are thermalized. The rate coefficient of the thermal dissociation of HOCH_2CH(O)CH_3 was also theoretically evaluated; the results at 1 atm in the 220-300 K range can be expressed as k_infinity = 3.5 * 10~(13) exp (-7.91 kcal mol~(-1)/(RT)) s~(-1) and k_(latm) = 3.6 * 10~(12) exp(-7.05 kcal mol~(-1)/(RT)) s~(-1). Thus, dissociation is also found to be the dominant fate of the thermalized oxy radicals.
机译：在与大气有关的条件下，在氮氧化物存在下，进行了OH引发的丙烯氧化的环境室研究。在研究的所有温度下（220-300 K）观察到的主要产物是CH_2O和CH_3CHO，表明在氧化过程中形成的＃beta＃-羟基丙氧基自由基（来自相应的＃beta＃-羟基丙基过氧自由基与NO的反应）主要经历单分子分解。已经对占主导地位的＃beta＃-羟丙基过氧，＃beta＃-羟丙基过氧亚硝酸盐和＃beta＃-羟基丙氧基的化学性质进行了完整的理论研究。根据B3L YP-DFT / 6-31G〜（**）量子化学特征，发现最稳定的氧自由基构象含有分子内氢键，可提供约2 kcal / mol的稳定度。发现能量最低的氧种中的内部氢键在C-C键断裂的过渡态中持续存在，这使它们分解的障碍降至7.2 kcal / mol。利用SSE理论，确定了新生的HOCH_2CH（O）CH_3氧自由基的内能分布;结果发现，大多数自由基的内在能量远高于其分解所计算出的势垒。因此，通过主方程分析确定，这些氧自由基中的大部分（在300 K和1 atm处为80％，在220 K和0.2 atm处为75％）将在碰撞稳定之前迅速分解，生成CH_2OH和CH_3CHO，其余为热化的。理论上评估了HOCH_2CH（O）CH_3的热解离速率系数; 1 atm在220-300 K范围内的结果可以表示为k_infinity = 3.5 * 10〜（13）exp（-7.91 kcal mol〜（-1）/（RT））s〜（-1）和k_（ latm）= 3.6 * 10〜（12）exp（-7.05 kcal mol〜（-1）/（RT））s〜（-1）。因此，也发现离解是热化氧自由基的主要命运。

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