Combustion Research Facility, Mail Stop 9055, Sandia National Laboratories, Livermore, CA 94551-0969, USA.
Science. 2015 Feb 6;347(6222):643-6. doi: 10.1126/science.aaa1495.
Oxidation of organic compounds in combustion and in Earth's troposphere is mediated by reactive species formed by the addition of molecular oxygen (O2) to organic radicals. Among the most crucial and elusive of these intermediates are hydroperoxyalkyl radicals, often denoted "QOOH." These species and their reactions with O2 are responsible for the radical chain branching that sustains autoignition and are implicated in tropospheric autoxidation that can form low-volatility, highly oxygenated organic aerosol precursors. We report direct observation and kinetics measurements of a QOOH intermediate in the oxidation of 1,3-cycloheptadiene, a molecule that offers insight into both resonance-stabilized and nonstabilized radical intermediates. The results establish that resonance stabilization dramatically changes QOOH reactivity and, hence, that oxidation of unsaturated organics can produce exceptionally long-lived QOOH intermediates.
有机化合物在燃烧和地球对流层中的氧化是由分子氧（O2）加成到有机自由基形成的活性物质介导的。在这些中间产物中，最重要和最难捉摸的是过氧烷基自由基，通常表示为“QOOH”。这些物质及其与 O2 的反应负责维持自动点火的自由基链分支，并且与可以形成低挥发性、高度含氧的有机气溶胶前体的对流层自动氧化有关。我们报告了在 1,3-环庚二烯氧化中 QOOH 中间体的直接观察和动力学测量，该分子提供了对共振稳定和非稳定自由基中间体的深入了解。结果表明，共振稳定极大地改变了 QOOH 的反应性，因此，不饱和有机物的氧化可以产生异常长寿命的 QOOH 中间体。
