Hsin Hong Yuan, Elrod Matthew J
Department of Chemistry and Biochemistry, Oberlin College, Oberlin, Ohio 44074, USA.
J Phys Chem A. 2007 Feb 1;111(4):613-9. doi: 10.1021/jp0665574.
The overall rate constants of the reactions of NO with hydroxy- and chloroalkylperoxy radicals, derived from the OH- and Cl-initiated oxidation of methacrolein and methyl vinyl ketone, respectively, were directly determined for the first time using the turbulent-flow technique and pseudo-first-order kinetics conditions with high-pressure chemical ionization mass spectrometry for the direct detection of peroxy radical reactants. The individual 100 Torr, 298 K hydroxyalkylperoxy + NO rate constants for the methacrolein [(0.93 +/- 0.12) (2sigma) x 10(-11) cm3 molecule(-1) s(-1)] and methyl vinyl ketone [(0.84 +/- 0.10) x 10(-11) cm3 molecule(-1) s(-1)] systems were found to be identical within the 95% confidence interval associated with each separate measurement, as were the chloroalkylperoxy + NO rate constants for both methacrolein [(1.17 +/- 0.11) x 10(-11) cm3 molecule(-1) s(-1)] and methyl vinyl ketone [(1.14 +/- 0.14) x 10(-11) cm3 molecule(-1) s(-1)]. However, the difference in the rate constants between the hydroxyperoxy + NO and chloroalkylperoxy + NO systems was found to be statistically significant, with the chloroalkylperoxy + NO rate constants about 30% higher than the corresponding hydroxyalkylperoxy + NO rate constants. This substituent effect was rationalized via a frontier molecular orbital model approach.
首次使用湍流技术和伪一级动力学条件，并结合高压化学电离质谱法直接检测过氧自由基反应物，直接测定了分别由甲基丙烯醛和甲基乙烯基酮的OH引发氧化和Cl引发氧化产生的NO与羟基和氯代烷基过氧自由基反应的总速率常数。在与每次单独测量相关的95%置信区间内，发现甲基丙烯醛体系[(0.93±0.12)(2σ)×10⁻¹¹ cm³ 分子⁻¹ s⁻¹]和甲基乙烯基酮体系[(0.84±0.10)×10⁻¹¹ cm³ 分子⁻¹ s⁻¹]的100 Torr、298 K时的羟基烷基过氧 + NO速率常数相同，甲基丙烯醛[(1.17±0.11)×10⁻¹¹ cm³ 分子⁻¹ s⁻¹]和甲基乙烯基酮[(1.14±0.14)×10⁻¹¹ cm³ 分子⁻¹ s⁻¹]的氯代烷基过氧 + NO速率常数也相同。然而，发现羟基过氧 + NO和氯代烷基过氧 + NO体系之间的速率常数差异具有统计学意义，氯代烷基过氧 + NO速率常数比相应的羟基烷基过氧 + NO速率常数高约30%。通过前沿分子轨道模型方法对这种取代基效应进行了合理解释。
