| 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" |
| 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" |
| 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" |
