%0 Journal Article
%A Barber, Victoria
P.
%A Pandit, Shubhrangshu
%A Green, Amy M.
%A Trongsiriwat, Nisalak
%A Walsh, Patrick J.
%A Klippenstein, Stephen J.
%A Lester, Marsha I.
%D 2018
%T Four-Carbon
Criegee Intermediate from Isoprene Ozonolysis:
Methyl Vinyl Ketone Oxide Synthesis, Infrared Spectrum, and OH Production
%U https://acs.figshare.com/articles/journal_contribution/Four-Carbon_Criegee_Intermediate_from_Isoprene_Ozonolysis_Methyl_Vinyl_Ketone_Oxide_Synthesis_Infrared_Spectrum_and_OH_Production/6985247
%R 10.1021/jacs.8b06010.s001
%2 https://acs.figshare.com/ndownloader/files/12810812
%K Criegee intermediates control
%K RR
%K unimolecular decay pathways
%K OO
%K OH products
%K unimolecular decay rate
%K master equation modeling yields
%K Methyl Vinyl Ketone Oxide Synthesis
%K IR absorption spectra
%K CH
%K Four-Carbon Criegee Intermediate
%K carbonyl oxide species
%K MACR-OO
%K hydrogen atom transfer mechanism
%K MVK-OO
%X 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 (CH2OO), methyl vinyl ketone oxide (MVK-OO), and
methacrolein oxide (MACR-OO). The nature of the substituents (R,R′
= H, CH3, CHCH2) 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 O2. 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.
%I ACS Publications