Computational Studies of the Isomerization and Hydration Reactions of Acetaldehyde Oxide and Methyl Vinyl Carbonyl Oxide

Abstract

Alkene ozonolysis is a major source of hydroxyl radical (*OH), the most important oxidant in the troposphere. Previous experimental and computational work suggests that for many alkenes the measured *OH yields should be attributed to the combined impact of both chemically activated and thermalized syn-alkyl Criegee intermediates (CIs), even though the thermalized CI should be susceptible to trapping by molecules such as water. We have used RRKM/master equation and variational transition state theory calculations to quantify the competition between unimolecular isomerization and bimolecular hydration reactions for the syn and anti acetaldehyde oxide formed in trans-2-butene ozonolysis and for the CIs formed in isoprene ozonolysis possessing syn-methyl groups. Statistical rate theory calculations were based on quantum chemical data provided by the B3LYP, QCISD, and multicoefficient G3 methods, and thermal rate constants were corrected for tunneling effects using the Eckart method. At tropospheric temperatures and pressures, all thermalized CIs with syn-methyl groups are predicted to undergo 1,4-hydrogen shifts from 2 to 8 orders of magnitude faster than they react with water monomer at its saturation number density. For thermalized anti acetaldehyde oxide, the rates of dioxirane formation and hydration should be comparable.

Atmospheric isoprene ozonolysis: impacts of stabilised Criegee intermediate reactions with SO<sub>2</sub>, H<sub>2</sub>O and dimethyl sulfide

“…with the terminal oxygen of the carbonyl oxide moiety on the same side as a hydrogen group) react relatively fast with H 2 O. This difference has been predicted theoretically (Kuwata et al, 2010;Anglada et al, 2011) and was subsequently confirmed in recent experiments (Taatjes et al, 2013; for the two CH 3 CHOO conformers. Additionally, it has been predicted theoretically (Vereecken et al, 2012) that the relative reaction rate constants for the water dimer vs. water monomer, k(SCI + (H 2 O) 2 )/k(SCI + H 2 O) of larger SCIs (except syn-CH 3 CHOO) will be over 70 times smaller than that for CH 2 OO, suggesting that reaction with the water dimer is unlikely to be the dominant fate for these SCIs under atmospheric conditions.…”

“…Chao et al, 2015;Lewis et al, 2015) have demonstrated a quadratic dependence of CH 2 OO loss on [H 2 O], suggesting a dominant role for the water dimer, (H 2 O) 2 , in CH 2 OO loss at typical atmospheric boundary layer H 2 O concentrations. For larger SCIs, both experimental (Taatjes et al, 2013;Newland et al, 2015) and theoretical (Kuwata et al, 2010;Anglada et al, 2011) studies have shown that their kinetics, in particular reaction with water, are highly structure dependent. syn-SCIs (i.e.…”

Kinetics of a Criegee intermediate that would survive high humidity and may oxidize atmospheric SO 2

“…1) does. Quantum-chemical investigations (25)(26)(27) as well as studies of alkene ozonolysis (20,28) SO 2 , these CIs may accumulate to higher concentrations and have higher probability to oxidize atmospheric SO 2 . Table 1 shows selected rate coefficients for relevant CI reactions and the effective first-order decay rate coefficients (k eff ) of small CIs under an atmospheric condition.…”

“…Quantum-chemistry (25)(26)(27) calculations predicted that the antiform of CIs (CIs with R 1 = H in Fig. 1, including CH 2 OO) react with water vapor very quickly and that the syn-form of CIs (CIs with R 1 ≠ H in Fig.…”

Overview of the Focused Isoprene eXperiment at the California Institute of Technology (FIXCIT): mechanistic chamber studies on the oxidation of biogenic compounds

“…The subsequent reactions of sCIs produce both carbonyl products and non-carbonyl products such as hydroperoxides. The syn and anti conformers of CIs and sCI can have substantially different reactivities (Kuwata et al, 2010;Anglada et al, 2011), with syn conformers more likely to decompose unimolecularly, possibly through a vinyl hydroperoxide intermediate .…”