Infrared Spectrum of the Adduct 2-Chloro-2-hydroperoxybut-3-ene [(C₂H₃)CCl(CH₃)OOH] of the Reaction between the Criegee Intermediate Methyl Vinyl Ketone Oxide [C₂H₃C(CH₃)OO] and HCl

Methyl vinyl ketone oxide (MVKO, C₂H₃C(CH₃)OO) is an important Criegee intermediate produced from ozonolysis of isoprene, which is the most abundant nonmethane hydrocarbon emitted into the atmosphere. Reactions between Criegee intermediate and hydrogen chloride (HCl) are important because of their large rate coefficients. In this work, we photolyzed a mixture of (<i>Z</i>)-(CH₂I)HC═C(CH₃)I/HCl/O₂ at 248 nm to produce MVKO to carry out the reaction MVKO + HCl and recorded infrared spectra of transient species with a step-scan Fourier-transform infrared absorption spectrometer. Eleven bands near 1415, 1381, 1350, 1249, 1178, 1118, 1103, 1065, 978, 931, and 895 cm^-1 were observed and assigned to the hydrogen-transferred adduct (C₂H₃)CCl(CH₃)OOH (2-chloro-2-hydroperoxybut-3-ene, CHPB) according to the predicted IR spectrum using the B3LYP/aug-cc-pVTZ method; the conformation could not be definitively determined. According to calculations, most low-energy conformers can interconvert, and the most stable conformers <i>anti</i>-<i>trans</i>-CHPB and <i>syn</i>-<i>trans</i>-CHPB might have the major contributions. Four bands near 1423, 1360, 1220, and 1080 cm^-1 were observed and tentatively assigned to the OH-decomposition products (C₂H₃)CCl(CH₃)O (1-chloro-1-methyl-2-propenyloxy, CMP); both <i>trans</i>-CMP and <i>cis</i>-CMP might contribute. Unlike in the case of CH₂OO + HCl and CH₃CHOO + HCl, in which secondary reactions of the OH-decomposition products reacted readily with O₂ to produce the dehydrated products HC(O)Cl and CH₃C(O)Cl, respectively, the secondary reaction of CMP with O₂ was not observed because there is no feasible H atom in CMP for O₂ to abstract.