Synthesis, electronic spectroscopy and photochemistry of methacrolein oxide: A four carbon unsaturated Criegee intermediate from isoprene ozonolysis,Journal of the American Chemical Society

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Synthesis, electronic spectroscopy and photochemistry of methacrolein oxide: A four carbon unsaturated Criegee intermediate from isoprene ozonolysis
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2019-08-26 , DOI: 10.1021/jacs.9b05193
Michael F Vansco ₁ , Barbara Marchetti ₁ , Nisalak Trongsiriwat ₁ , Trisha Bhagde ₁ , Guanghan Wang ₁ , Patrick J Walsh ₁ , Stephen J Klippenstein ₂ , Marsha I Lester ₁

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Ozonolysis of isoprene, one of the most abundant volatile organic compounds in the Earth's atmosphere, generates the four-carbon unsaturated methacrolein oxide (MACR-oxide) Criegee intermediate. The first laboratory synthesis and direct detection of MACR-oxide is achieved through reaction of photolytically generated, resonance-stabilized iodoalkene radicals with oxygen. MACR-oxide is characterized on its first π*←π electronic transition using a ground state depletion method. MACR-oxide exhibits a broad UV-visible spectrum peaked at 380 nm with weak oscillatory structure at long wavelengths ascribed to vibrational resonances. Complementary theory predicts two strong π*←π transitions arising from extended conjugation across MACR-oxide with overlapping contributions from its four conformers. Electronic promotion to the 11ππ* state agrees well with experiment, and results in nonadiabatic coupling and prompt release of O 1D products observed as anisotropic velocity map images. This sensitive detection scheme will enable study of its unimolecular and bimolecular reactions under atmospheric conditions.

中文翻译：

氧化甲基丙烯醛的合成、电子光谱和光化学：来自异戊二烯臭氧分解的四碳不饱和 Criegee 中间体

异戊二烯（地球大气中含量最丰富的挥发性有机化合物之一）的臭氧分解生成四碳不饱和甲基丙烯醛氧化物（MACR-氧化物）Criegee 中间体。MACR-氧化物的首次实验室合成和直接检测是通过光解产生的、共振稳定的碘代烯烃自由基与氧的反应来实现的。MACR-氧化物的特征在于其使用基态耗尽方法的第一个 π*←π 电子跃迁。MACR-氧化物表现出宽的紫外可见光谱，峰值为 380 nm，在长波长处具有弱振荡结构，归因于振动共振。互补理论预测两个强烈的 π*←π 跃迁由跨越 MACR 氧化物的扩展共轭引起，其四个构象异构体的重叠贡献。电子提升到 11ππ* 状态与实验非常吻合，并导致非绝热耦合和 O 1D 产物的迅速释放，观察为各向异性速度图图像。这种灵敏的检测方案将能够研究其在大气条件下的单分子和双分子反应。

更新日期：2019-08-26

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