Infrared characterization of formation and resonance stabilization of the Criegee intermediate methyl vinyl ketone oxide.

Methyl vinyl ketone oxide (MVKO) is an important Criegee intermediate in the ozonolysis of isoprene. MVKO is resonance stabilized by its allyl moiety, but no spectral characterization of this stabilization was reported to date. In this study, we photolyzed a mixture of 1,3-diiodo-but-2-ene and O 2 to produce MVKO and characterized the syn-trans-MVKO, and tentatively syn-cis-MVKO, with transient infrared spectra recorded using a step-scan Fourier-transform spectrometer. The O‒O stretching band at 948 cm -1 of syn-trans-MVKO is much greater than the corresponding bands of syn-CH 3 CHOO and (CH 3 ) 2 COO Criegee intermediates at 871 and 887 cm -1 , respectively, confirming a stronger O‒O bond due to resonance stabilization. We observed also iodoalkenyl radical C 2 H 3 C(CH 3 )I upon photolysis of the precursor to confirm the fission of the terminal allylic C‒I bond rather than the central vinylic C‒I bond of the precursor upon photolysis. At high pressure, the adduct C 2 H 3 C(CH 3 )IOO was also observed. The reaction mechanism is characterized.