Ozonolysis of Cyclic Alkenes as Surrogates for Biogenic Terpenes: Primary Ozonide Formation and Decomposition

Abstract

Alkene ozonolysis reactions proceed through an unstable intermediate, the primary ozonide (POZ). POZ decomposition controls the complex mechanism. We probe the kinetics of primary ozonide decomposition using temperature programmed reaction spectroscopy (TPRS), revealing primary ozonide decomposition barrier heights of 9.1 +/- 0.4, 9.4 +/- 0.4, and 11.9 +/- 1.2 kcal mol(-1) for cyclohexene, 1-methyl-cyclohexene, and methylene-cyclohexane, respectively. We compare experimental decomposition spectra with spectral predictions using density functional theory (DFT) to reveal decomposition products resembling vinyl-hydroperoxides and dioxiranes. We do not find evidence of secondary ozonides. Additional computations with DFT, scaled with the TPRS barrier height, yield barrier heights ranging from 9.4 to 12.1 kcal mol(-1) for the four competing decomposition pathways of the 1-methyl-cyclohexene POZ. Entropic differences were minimal, indicating that POZ decomposition branching is controlled purely by enthalpic variations. These kinetic computations were used to calculate a hydroxyl radical yield for 1-methyl-cyclohexene ozonolysis of 0.85 at 298 K.

A Computational Study of the Ozonolysis of Phenanthrene

“…Furthermore, the bond length of O-O bond cleavage in TS 2 A is 2.109 Å, using B3LYP/6-31G(2df,p) method. In general, the bond lengths are in good agreement with the ozonolysis of monoterpenes [43][44][45].…”

Model–measurement comparison of functional group abundance in <i>α</i>-pinene and 1,3,5-trimethylbenzene secondary organic aerosol formation

“…Proposed dimerization reactions do not contribute to depletion of aCH bonds, and dimers produced in the aerosol phase have been found to have a similar O : C ratio to the monomer (Zhang et al, 2015). Photolysis of hydroperoxides has been suggested as a condensed-phase mechanism that leads to increase in naCO (Epstein et al, 2014), but an estimate based on the 6-day lifetime molar conversion of hydroperoxide groups to naCO only increases the latter fraction from 8 to 9 % of the FG mole fraction after 21 h (though naCO increases by 9 % over the case of no conversion) and does not fully explain the discrepancy between model and measurements for this FG. However, further oxidation due to dissolved oxidants, such as the OH radical, may reduce the proportion of aCH relative to oxidized groups, though this rate is also dependent on Table 3.…”

“…Our capability to simulate SOA formation is often evaluated against aerosol mass yield, O : C, carbon oxidation state, mean carbon number, volatility, and specific species or compound classes when available (e.g., Robinson et al, 2007;Kroll et al, 2011;Donahue et al, 2012;Nozière et al, 2015). These properties can be measured using various forms of mass spectrometry (e.g., Jayne et al, 2000;Jimenez et al, 2009;Nizkorodov et al, 2011) or through monitoring changes in size distribution in combination with isothermal dilution or thermal heating (e.g., Grieshop et al, 2009;Cappa, 2010;Epstein and Donahue, 2010;Donahue et al, 2012). Functional group (FG) composition is a complementary representation of organic molecules and complex organic mixtures that offers a balance between parsimony and chemical fidelity for measurement and interpretation.…”

Control of ozonolysis kinetics and aerosol yield by nuances in the molecular structure of volatile organic compounds

“…Relationships between VOC molecular structure and SOA yield have been reported for a number of chemical systems. Some studies identify surrogates for naturally occurring VOCs, 10,38 some catalog the SOA yield of several compounds, 9,13,37,39 while others identify key molecular structures that influence SOA yield. 10,14,[24][25][26]40 Most studies to date have focused on linear, branched and cyclic alkanes or cycloalkenes.…”