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Direct observation and kinetics of a hydroperoxyalkyl radical (QOOH)

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Science  06 Feb 2015:
Vol. 347, Issue 6222, pp. 643-646
DOI: 10.1126/science.aaa1495

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Catching a glimpse of the elusive QOOH

It's straightforward to write down the net combustion reaction: Oxygen reacts with hydrocarbons to form water and carbon dioxide. The details of how all the bonds break and form in succession are a great deal more complicated. Savee et al. now report direct detection of a long-postulated piece of the puzzle, a so-called QOOH intermediate. This structure results from bound oxygen stripping a hydrogen atom from carbon, leaving a carbon-centered radical behind. The study explores the influence of the hydrocarbon's unsaturation on the stability of QOOH, which has implications for both combustion and tropospheric oxidation chemistry.

Science, this issue p. 643

Abstract

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.

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