Double Bonds Are Key to Fast Unimolecular Reactivity in First-Generation Monoterpene Hydroxy Peroxy Radicals

Monoterpenes are a group of volatile organic compounds that are emitted to the atmosphere in large amounts by natural sources. Some monoterpenes such as limonene and &#916;3-carene are also widely used as additives in detergents and perfumes, and thus have a potential impact on indoor air quality and human health.The volatile organic compounds like monoterpenes may undergo a series of autoxidation processes in the atmosphere to form highly oxygenated compounds, which have been linked to the formation of secondary organic aerosols. For this process to occur, the unimolecular reactions of the peroxy radicals formed during oxidation must have rate coefficients comparable to or greater than those of the competing bimolecular reactions with HO2, NO or other RO2 radicals.We studied the hydrogen shift (H-shift) and the cyclization reactions of all 45 hydroxy peroxy radicals formed by hydroxyl radical (OH) and O2 addition to six monoterpenes (&#945;-pinene, &#946;-pinene, &#916;3-carene, camphene, limonene and terpinolene). The reaction rate coefficients of the possible unimolecular reaction were initially studied at a lower level of theory. Those deemed likely to be atmospherically competitive were then calculated using the multi-conformer transition states theory approach developed by M&#248;ller et al. (J. Phys. Chem. A, 120, 51, 10072-10087, 2016). This approach has been shown to agree with the experimental values to within a factor of 4 for other systems.It was found that double bonds are key to fast unimolecular reactions in the first-generation monoterpene hydroxy peroxy radicals. The H-shift reactions abstracting a hydrogen from a carbon adjacent to a double bond are found to typically be fast enough to compete with the bimolecular reactions, likely due to the resonance stability of the nascent allylic radical. The reactivity of the cyclization reaction between the carbon-carbon double bonds and the peroxy group, which forms an endoperoxide ring, is high as well. The H-shifts abstracting the hydrogen from the hydroxy group may be competitive in some cases but the reaction rate coefficients for these reactions are more uncertain. Generally, the cyclization reaction and the allylic H-shift reactions are the dominant reaction paths for the studied peroxyl radicals. Since the OH radical addition consumes one double bond, we suggest that the monoterpenes with more than one double bond in their structure are likely to have unimolecular reactions that can be important for the first-generation monoterpene peroxy radicals. On the other hand, the ones with only one double bond initially are not likely to have fast unimolecular reactions that can compete with the bimolecular reactions under the atmospheric condition, unless a double bond can be formed during their oxidation process as found for &#945;-pinene and &#946;-pinene. This result greatly limits the amount of potentially important unimolecular reaction paths in atmospheric monoterpene oxidation.

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Highly oxygenated organic molecules (HOM) formation in the isoprene oxidation by NO3 radical

10.5194/acp-2020-1178 ◽

2020 ◽

Author(s):

Defeng Zhao ◽

Iida Pullinen ◽

Hendrik Fuchs ◽

Stephanie Schrade ◽

Rongrong Wu ◽

...

Keyword(s):

Double Bond ◽

First Generation ◽

Second Generation ◽

Organic Molecules ◽

Closed Shell ◽

Direct Reaction ◽

Peroxy Radicals ◽

Night Time ◽

Time Profiles ◽

Carbon Double Bond

Abstract. Highly oxygenated organic molecules (HOM) are found to play an important role in the formation and growth of secondary organic aerosol (SOA). SOA is an important type of aerosol with significant impact on air quality and climate. Compared with the oxidation of volatile organic compounds by O3 and OH, HOM formation in the oxidation by NO3 radical, an important oxidant at night-time and dawn, has received less attention. In this study, HOM formation in the reaction of isoprene with NO3 was investigated in the SAPHIR chamber (Simulation of Atmospheric PHotochemistry In a large Reaction chamber). A large number of HOM including monomers (C5), dimers (C10), and trimers (C15), both closed-shell compounds and open-shell peroxy radicals, were identified and were classified into various series according to their formula. Their formation pathways were proposed based on the peroxy radicals observed and known mechanisms in the literature, which were further constrained by the time profiles of HOM after sequential isoprene addition to differentiate first- and second-generation products. HOM monomers containing one to three N atoms (1–3N monomers) were formed, starting with NO3 addition to carbon double bond, forming peroxy radicals (RO2), followed by autoxidation. 1N monomers were formed by both the direct reaction of NO3 with isoprene and of NO3 with first-generation products. 2N-monomers (e.g. C5H8N2On (n = 8–13), C5H10N2On (n = 8–14)) were likely the termination products of C5H9N2On•, which was formed by the addition of NO3 to C5-hydroxynitrate (C5H9NO4), a first-generation product containing one carbon double bond. 2N-monomers, which were second-generation products, dominated in monomers and accounted for ~34 % of all HOM, indicating the important role of second-generation oxidation in HOM formation in isoprene+NO3 under our reaction conditions. H-shift of alkoxy radicals to form peroxy radicals and subsequent autoxidation (alkoxy-peroxy pathway) was found to be an important pathway of HOM formation. HOM dimers were mostly formed by the accretion reaction of various HOM monomer RO2 and via the termination reactions of dimer RO2 formed by further reaction of closed-shell dimers with NO3 and possibly by the reaction of C5-RO2 with isoprene. HOM trimers were likely formed by the accretion reaction of dimer RO2 with monomer RO2. The concentrations of different HOM showed distinct time profiles during the reaction, which was linked to their formation pathway. HOM concentrations either showed a typical time profile of first-generation products, or of second-generation products, or a combination of both, indicating multiple formation pathways and/or multiple isomers. Total HOM molar yield was estimated to be 1.2 %+1.3 %−0.7 %, which corresponded to a SOA yield of ~3.6 % assuming the molecular weight of C5H9NO6 as the lower limit. This yield suggests that HOM may contribute a significant fraction to SOA yield in the reaction of isoprene with NO3.

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Biomass burning plume chemistry: OH radical initiated oxidation of 3-penten-2-one and its main oxidation product 2-hydroxypropanal

10.5194/acp-2021-575 ◽

2021 ◽

Author(s):

Niklas Illmann ◽

Iulia Patroescu-Klotz ◽

Peter Wiesen

Keyword(s):

Biomass Burning ◽

First Generation ◽

Rate Coefficient ◽

Reaction System ◽

Oh Radical ◽

Peroxy Radicals ◽

Methyl Glyoxal ◽

Experimental Conditions ◽

Temporal Behaviour ◽

Radical Yield

Abstract. In order to enlarge our understanding of biomass burning plume chemistry, the OH radical initiated oxidation of 3-penten-2-one (3P2), identified in biomass burning emissions, and 2-hydroxypropanal (2HPr) were investigated at 298 ± 3 K and 990 ± 15 mbar in two atmospheric simulation chambers using long-path FTIR spectroscopy. The rate coefficient of 3P2 + OH was determined to be (6.2 ± 1.0) × 10−11 cm3 molecule−1 s−1 and the molar first-generation yields for acetaldehyde, methyl glyoxal, 2HPr and the sum of PAN and CO2, used to determine the CH3C(O) radical yield, were 0.39 ± 0.07, 0.32 ± 0.08, 0.68 ± 0.27, and 0.56 ± 0.14, respectively, under conditions where the 3P2 derived peroxy radicals react solely with NO. The 2HPr + OH reaction was investigated using 3P2 + OH as a source of the α-hydroxyaldehyde adjusting the experimental conditions to shift the reaction system towards secondary oxidation processes. The rate coefficient was estimated to be (2.2 ± 0.6) × 10−11 cm3 molecule−1 s−1. Employing an Euler-Cauchy model to describe the temporal behaviour of the experiments, the further oxidation of 2HPr was shown to form methyl glyoxal, acetaldehyde and CO2 with estimated yields of 0.21 ± 0.05, 0.79 ± 0.05, and 0.79 ± 0.05, respectively.

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Modelling of the photooxidation of toluene: conceptual ideas for validating detailed mechanisms

Atmospheric Chemistry and Physics ◽

10.5194/acp-3-89-2003 ◽

2003 ◽

Vol 3 (1) ◽

pp. 89-106 ◽

Cited By ~ 41

Author(s):

V. Wagner ◽

M. E. Jenkin ◽

S. M. Saunders ◽

J. Stanton ◽

K Wirtz ◽

...

Keyword(s):

First Generation ◽

Chemical Mechanism ◽

Ozone Production ◽

Peroxy Radicals ◽

Reaction Systems ◽

Master Chemical Mechanism ◽

Reactive Nitrogen Oxides ◽

Toluene Photooxidation ◽

Radical Transformation ◽

Validation Experiments

Abstract. Toluene photooxidation is chosen as an example to examine how simulations of smog-chamber experiments can be used to unravel shortcomings in detailed mechanisms and to provide information on complex reaction systems that will be crucial for the design of future validation experiments. The mechanism used in this study is extracted from the Master Chemical Mechanism Version 3 (MCM v3) and has been updated with new modules for cresol and g-dicarbonyl chemistry. Model simulations are carried out for a toluene-NOx experiment undertaken at the European Photoreactor (EUPHORE). The comparison of the simulation with the experimental data reveals two fundamental shortcomings in the mechanism: OH production is too low by about 80%, and the ozone concentration at the end of the experiment is over-predicted by 55%. The radical budget was analysed to identify the key intermediates governing the radical transformation in the toluene system. Ring-opening products, particularly conjugated g-dicarbonyls, were identified as dominant radical sources in the early stages of the experiment. The analysis of the time evolution of radical production points to a missing OH source that peaks when the system reaches highest reactivity. First generation products are also of major importance for the ozone production in the system. The analysis of the radical budget suggests two options to explain the concurrent under-prediction of OH and over-prediction of ozone in the model: 1) missing oxidation processes that produce or regenerate OH without or with little NO to NO2 conversion or 2) NO3 chemistry that sequesters reactive nitrogen oxides into stable nitrogen compounds and at the same time produces peroxy radicals. Sensitivity analysis was employed to identify significant contributors to ozone production and it is shown how this technique, in combination with ozone isopleth plots, can be used for the design of validation experiments.

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Selective ring-opening metathesis polymerization (ROMP) of cyclobutenes. Unsymmetrical ladderphane containing polycyclobutene and polynorbornene strands

Beilstein Journal of Organic Chemistry ◽

10.3762/bjoc.15.4 ◽

2019 ◽

Vol 15 ◽

pp. 44-51 ◽

Cited By ~ 3

Author(s):

Yuan-Zhen Ke ◽

Shou-Ling Huang ◽

Guoqiao Lai ◽

Tien-Yau Luh

Keyword(s):

Methyl Ester ◽

Ambient Temperature ◽

Ring Opening ◽

First Generation ◽

Double Bonds ◽

Ring Opening Metathesis Polymerization ◽

Metathesis Polymerization ◽

Selective Ring Opening ◽

Norbornene Derivatives

At 0 °C in THF in the presence of Grubbs first generation catalyst, cyclobutene derivatives undergo ROMP readily, whereas norbornene derivatives remain intact. When the substrate contains both cyclobutene and norbornene moieties, the conditions using THF as the solvent at 0 °C offer a useful protocol for the selective ROMP of cyclobutene to give norbornene-appended polycyclobutene. Unsymmetrical ladderphane having polycyclobutene and polynorbornene as two strands is obtained by further ROMP of the norbornene appended polycyclobutene in the presence of Grubbs first generation catalyst in DCM at ambient temperature. Methanolysis of this unsymmetrical ladderphane gives polycyclobutene methyl ester and insoluble polynorbornene-amide-alcohol. The latter is converted into the corresponding soluble acetate. Both polymers are well characterized by spectroscopic means. No norbornene moiety is found to be incorporated into polycyclobutene strand at all. The double bonds in the polycyclobutene strand are mainly in cis configuration (ca 70%), whereas the E/Z ratio for polynorbornene strand is 8:1.

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Biomass burning plume chemistry: OH-radical-initiated oxidation of 3-penten-2-one and its main oxidation product 2-hydroxypropanal

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-18557-2021 ◽

2021 ◽

Vol 21 (24) ◽

pp. 18557-18572

Author(s):

Niklas Illmann ◽

Iulia Patroescu-Klotz ◽

Peter Wiesen

Keyword(s):

Biomass Burning ◽

First Generation ◽

Rate Coefficient ◽

Reaction System ◽

Chemical Mechanism ◽

Oh Radical ◽

Peroxy Radicals ◽

Methyl Glyoxal ◽

Experimental Conditions ◽

Temporal Behaviour

Abstract. In order to enlarge our understanding of biomass burning plume chemistry, the OH-radical-initiated oxidation of 3-penten-2-one (3P2), identified in biomass burning emissions, and 2-hydroxypropanal (2HPr) was investigated at 298 ± 3 K and 990 ± 15 mbar in two atmospheric simulation chambers using long-path FTIR spectroscopy. The rate coefficient of 3P2 + OH was determined to be (6.2 ± 1.0) × 10−11 cm3 molec.−1 s−1 and the molar first-generation yields for acetaldehyde, methyl glyoxal, 2HPr, and the sum of peroxyacetyl nitrate (PAN) and CO2, used to determine the CH3C(O) radical yield, were 0.39 ± 0.07, 0.32 ± 0.08, 0.68 ± 0.27, and 0.56 ± 0.14, respectively, under conditions where the 3P2-derived peroxy radicals react solely with NO. The 2HPr + OH reaction was investigated using 3P2 + OH as a source of the α-hydroxyaldehyde adjusting the experimental conditions to shift the reaction system towards secondary oxidation processes. The rate coefficient was estimated to be (2.2 ± 0.6) × 10−11 cm3 molec.−1 s−1. Employing a simple chemical mechanism to analyse the temporal behaviour of the experiments, the further oxidation of 2HPr was shown to form methyl glyoxal, acetaldehyde, and CO2 with estimated yields of 0.27 ± 0.08, 0.73 ± 0.08, and 0.73 ± 0.08, respectively.

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α-pinene photooxidation under controlled chemical conditions – Part 1: Gas-phase composition in low- and high-NOx environments

Atmospheric Chemistry and Physics ◽

10.5194/acp-12-6489-2012 ◽

2012 ◽

Vol 12 (14) ◽

pp. 6489-6504 ◽

Cited By ~ 56

Author(s):

N. C. Eddingsaas ◽

C. L. Loza ◽

L. D. Yee ◽

J. H. Seinfeld ◽

P. O. Wennberg

Keyword(s):

Gas Phase ◽

Carboxylic Acids ◽

First Generation ◽

Peroxy Radical ◽

Organic Aerosol ◽

Oxidation Products ◽

Peroxy Radicals ◽

Alkoxy Radical ◽

Alkyl Peroxy Radicals ◽

Chemical Conditions

Abstract. The OH oxidation of α-pinene under both low- and high-NOx environments was studied in the Caltech atmospheric chambers. Ozone was kept low to ensure OH was the oxidant. The initial α-pinene concentration was 20–50 ppb to ensure that the dominant peroxy radical pathway under low-NOx conditions is reaction with HO2, produced from reaction of OH with H2O2, and under high-NOx conditions, reactions with NO. Here we present the gas-phase results observed. Under low-NOx conditions the main first generation oxidation products are a number of α-pinene hydroxy hydroperoxides and pinonaldehyde, accounting for over 40% of the yield. In all, 65–75% of the carbon can be accounted for in the gas phase; this excludes first-generation products that enter the particle phase. We suggest that pinonaldehyde forms from RO2 + HO2 through an alkoxy radical channel that regenerates OH, a mechanism typically associated with acyl peroxy radicals, not alkyl peroxy radicals. The OH oxidation and photolysis of α-pinene hydroxy hydroperoxides leads to further production of pinonaldehyde, resulting in total pinonaldehyde yield from low-NOx OH oxidation of ~33%. The low-NOx OH oxidation of pinonaldehyde produces a number of carboxylic acids and peroxyacids known to be important secondary organic aerosol components. Under high-NOx conditions, pinonaldehyde was also found to be the major first-generation OH oxidation product. The high-NOx OH oxidation of pinonaldehyde did not produce carboxylic acids and peroxyacids. A number of organonitrates and peroxyacyl nitrates are observed and identified from α-pinene and pinonaldehyde.

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Unusually Fast 1,6-H Shifts of Enolic Hydrogens in Peroxy Radicals: Formation of the First-Generation C2 and C3 Carbonyls in the Oxidation of Isoprene

The Journal of Physical Chemistry A ◽

10.1021/jp211447q ◽

2012 ◽

Vol 116 (24) ◽

pp. 6134-6141 ◽

Cited By ~ 23

Author(s):

Jozef Peeters ◽

Thanh Lam Nguyen

Keyword(s):

First Generation ◽

Peroxy Radicals

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Highly oxygenated organic molecule (HOM) formation in the isoprene oxidation by NO3 radical

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-9681-2021 ◽

2021 ◽

Vol 21 (12) ◽

pp. 9681-9704

Author(s):

Defeng Zhao ◽

Iida Pullinen ◽

Hendrik Fuchs ◽

Stephanie Schrade ◽

Rongrong Wu ◽

...

Keyword(s):

Double Bond ◽

First Generation ◽

Second Generation ◽

Closed Shell ◽

Time Profile ◽

Direct Reaction ◽

Peroxy Radicals ◽

Experimental Conditions ◽

Time Profiles ◽

Carbon Double Bond

Abstract. Highly oxygenated organic molecules (HOM) are found to play an important role in the formation and growth of secondary organic aerosol (SOA). SOA is an important type of aerosol with significant impact on air quality and climate. Compared with the oxidation of volatile organic compounds by ozone (O3) and hydroxyl radical (OH), HOM formation in the oxidation by nitrate radical (NO3), an important oxidant at nighttime and dawn, has received less attention. In this study, HOM formation in the reaction of isoprene with NO3 was investigated in the SAPHIR chamber (Simulation of Atmospheric PHotochemistry In a large Reaction chamber). A large number of HOM, including monomers (C5), dimers (C10), and trimers (C15), both closed-shell compounds and open-shell peroxy radicals (RO2), were identified and were classified into various series according to their formula. Their formation pathways were proposed based on the peroxy radicals observed and known mechanisms in the literature, which were further constrained by the time profiles of HOM after sequential isoprene addition to differentiate first- and second-generation products. HOM monomers containing one to three N atoms (1–3N-monomers) were formed, starting with NO3 addition to carbon double bond, forming peroxy radicals, followed by autoxidation. 1N-monomers were formed by both the direct reaction of NO3 with isoprene and of NO3 with first-generation products. 2N-monomers (e.g., C5H8N2On(n=7–13), C5H10N2On(n=8–14)) were likely the termination products of C5H9N2On⚫, which was formed by the addition of NO3 to C5-hydroxynitrate (C5H9NO4), a first-generation product containing one carbon double bond. 2N-monomers, which were second-generation products, dominated in monomers and accounted for ∼34 % of all HOM, indicating the important role of second-generation oxidation in HOM formation in the isoprene + NO3 reaction under our experimental conditions. H shift of alkoxy radicals to form peroxy radicals and subsequent autoxidation (“alkoxy–peroxy” pathway) was found to be an important pathway of HOM formation. HOM dimers were mostly formed by the accretion reaction of various HOM monomer RO2 and via the termination reactions of dimer RO2 formed by further reaction of closed-shell dimers with NO3 and possibly by the reaction of C5–RO2 with isoprene. HOM trimers were likely formed by the accretion reaction of dimer RO2 with monomer RO2. The concentrations of different HOM showed distinct time profiles during the reaction, which was linked to their formation pathway. HOM concentrations either showed a typical time profile of first-generation products, second-generation products, or a combination of both, indicating multiple formation pathways and/or multiple isomers. Total HOM molar yield was estimated to be 1.2 %-0.7%+1.3%, which corresponded to a SOA yield of ∼3.6 % assuming the molecular weight of C5H9NO6 as the lower limit. This yield suggests that HOM may contribute a significant fraction to SOA yield in the reaction of isoprene with NO3.

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The role of radical chemistry in the product formation from nitrate radical initiated gas-phase oxidation of isoprene

10.5194/egusphere-egu21-7338 ◽

2021 ◽

Author(s):

Philip T. M. Carlsson ◽

Luc Vereecken ◽

Anna Novelli ◽

François Bernard ◽

Birger Bohn ◽

...

Keyword(s):

Gas Phase ◽

First Generation ◽

Product Distribution ◽

Chem Phys ◽

Oxidation Products ◽

Rate Coefficients ◽

Peroxy Radicals ◽

Model Calculations ◽

Alkoxy Radicals ◽

Wide Range

Experiments at atmospherically relevant conditions were performed in the simulation chamber SAPHIR, investigating the reaction of isoprene with NO3 and its subsequent oxidation. Due to the production of NO3 from the reaction of NO2 with O3 as well as the formation of OH in subsequent reactions, the reactions of isoprene with O3 and OH were estimated to contribute up to 15% of the total isoprene consumption each in these experiments. The ratio of RO2 to HO2 concentrations was varied by changing the reactant concentrations, which modifies the product distribution from bimolecular reactions of the nitrated RO2. The reaction with HO2 or NO3 was found to be the main bimolecular loss process for the RO2 radicals under all conditions examined.Yields of the first-generation isoprene oxygenated nitrates as well as the sum of methyl vinyl ketone (MVK) and methacrolein (MACR) were determined by high resolution proton mass spectrometry using the Vocus PTR-TOF. The experimental time series of these products are compared to model calculations based on the MCM v3.3.1,1 the isoprene mechanism as published by Wennberg et al.2 and the newly developed FZJ-NO3-isoprene mechanism,3 which incorporates theory-based rate coefficients for a wide range of reactions.Among other changes, the FZJ-NO3-isoprene mechanism contains a novel fast oxidation route through the epoxidation of alkoxy radicals, originating from the formation of nitrated peroxy radicals. This inhibits the formation of MVK and MACR from the NO3-initiated oxidation of isoprene to practically zero, which agrees with the observations from chamber experiments. In addition, the FZJ-NO3-isoprene mechanism increases the level of agreement for the main first-generation oxygenated nitrates.&#160;1 M. E. Jenkin, J. C. Young and A. R. Rickard, The MCM v3.3.1 degradation scheme for isoprene, Atmospheric Chem. Phys., 2015, 15, 11433&#8211;11459.2 P. O. Wennberg at al., Gas-Phase Reactions of Isoprene and Its Major Oxidation Products, Chem. Rev., 2018, 118, 3337&#8211;3390.&#160;3 L. Vereecken et al., Theoretical and experimental study of peroxy and alkoxy radicals in the NO3-initiated oxidation of isoprene, Phys. Chem. Chem. Phys., submitted.

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Double Bonds Are Key to Fast Unimolecular Reactivity in First-Generation Monoterpene Hydroxy Peroxy Radicals