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J Am Chem Soc


Title:"Four-Carbon Criegee Intermediate from Isoprene Ozonolysis: Methyl Vinyl Ketone Oxide Synthesis, Infrared Spectrum, and OH Production"
Author(s):Barber VP; Pandit S; Green AM; Trongsiriwat N; Walsh PJ; Klippenstein SJ; Lester MI;
Address:"Department of Chemistry , University of Pennsylvania , Philadelphia , Pennsylvania 19104-6323 , United States. Chemical Sciences and Engineering Division , Argonne National Laboratory , Argonne , Illinois 60439 , United States"
Journal Title:J Am Chem Soc
Year:2018
Volume:20180820
Issue:34
Page Number:10866 - 10880
DOI: 10.1021/jacs.8b06010
ISSN/ISBN:1520-5126 (Electronic) 0002-7863 (Linking)
Abstract:"The reaction of ozone with isoprene, one of the most abundant volatile organic compounds in the atmosphere, produces three distinct carbonyl oxide species (RR'COO) known as Criegee intermediates: formaldehyde oxide (CH(2)OO), methyl vinyl ketone oxide (MVK-OO), and methacrolein oxide (MACR-OO). The nature of the substituents (R,R' = H, CH(3), CH horizontal lineCH(2)) and conformations of the Criegee intermediates control their subsequent chemistry in the atmosphere. In particular, unimolecular decay of MVK-OO is predicted to be the major source of hydroxyl radicals (OH) in isoprene ozonolysis. This study reports the initial laboratory synthesis and direct detection of MVK-OO through reaction of a photolytically generated, resonance-stabilized monoiodoalkene radical with O(2). MVK-OO is characterized utilizing infrared (IR) action spectroscopy, in which IR activation of MVK-OO with two quanta of CH stretch at ca. 6000 cm(-1) is coupled with ultraviolet detection of the resultant OH products. MVK-OO is identified by comparison of the experimentally observed IR spectral features with theoretically predicted IR absorption spectra. For syn-MVK-OO, the rate of appearance of OH products agrees with the unimolecular decay rate predicted using statistical theory with tunneling. This validates the hydrogen atom transfer mechanism and computed transition-state barrier (18.0 kcal mol(-1)) leading to OH products. Theoretical calculations reveal an additional roaming pathway between the separating radical fragments, which results in other products. Master equation modeling yields a thermal unimolecular decay rate for syn-MVK-OO of 33 s(-1) (298 K, 1 atm). For anti-MVK-OO, theoretical exploration of several unimolecular decay pathways predicts that isomerization to dioxole is the most likely initial step to products"
Keywords:
Notes:"PubMed-not-MEDLINEBarber, Victoria P Pandit, Shubhrangshu Green, Amy M Trongsiriwat, Nisalak Walsh, Patrick J Klippenstein, Stephen J Lester, Marsha I eng Research Support, U.S. Gov't, Non-P.H.S. 2018/08/04 J Am Chem Soc. 2018 Aug 29; 140(34):10866-10880. doi: 10.1021/jacs.8b06010. Epub 2018 Aug 20"

 
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