Isomerization Of Radicals Research Articles

Spectroscopic identification of isomeric jet-cooled benzyl-type radicals formed from 3-fluoro-o-xylene by corona discharge

By means of a pinhole-type glass nozzle designed for supersonic jet expansion along with corona discharge, vibronically excited but jet-cooled isomeric benzyl-type radicals were generated from the precursor 3-fluoro-o-xylene. The visible vibronic emission spectrum was recorded from the discharge system with a long-path monochromator. From an analysis of the spectrum observed, we identified the formation of two isomers, 2-methyl-3-fluorobenzyl and 2-methyl-6-fluorobenzyl radicals in the corona discharge of precursor, and determined for the first time the electronic energy in the D1→D0 transition and vibrational mode frequencies in the D0 state for both isomers.

Low-Temperature Combustion Chemistry of n-Butanol: Principal Oxidation Pathways of Hydroxybutyl Radicals

Reactions of hydroxybutyl radicals with O2 were investigated by a combination of quantum-chemical calculations and experimental measurements of product formation. In pulsed-photolytic Cl-initiated oxidation of n-butanol, the time-resolved and isomer-specific product concentrations were probed using multiplexed tunable synchrotron photoionization mass spectrometry (MPIMS). The interpretation of the experimental data is underpinned by potential energy surfaces for the reactions of O2 with the four hydroxybutyl isomers (1-hydroxybut-1-yl, 1-hydroxybut-2-yl, 4-hydroxybut-2-yl, and 4-hydroxybut-1-yl) calculated at the CBS-QB3 and RQCISD(T)/cc-pV∞Z//B3LYP/6-311++G(d,p) levels of theory. The observed product yields display substantial temperature dependence, arising from a competition among three fundamental pathways: (1) stabilization of hydroxybutylperoxy radicals, (2) bimolecular product formation in the hydroxybutyl + O2 reactions, and (3) decomposition of hydroxybutyl radicals. The 1-hydroxybut-1-yl + O2 reaction is dominated by direct HO2 elimination from the corresponding peroxy radical forming butanal as the stable coproduct. The chemistry of the other three hydroxybutylperoxy radical isomers mainly proceeds via alcohol-specific internal H-atom abstractions involving the H atom from either the -OH group or from the carbon attached to the -OH group. We observe evidence of the recently reported water elimination pathway (Welz et al. J. Phys. Chem. Lett. 2013, 4 (3), 350-354) from the 4-hydroxybut-2-yl + O2 reaction, supporting its importance in γ-hydroxyalkyl + O2 reactions. Experiments using the 1,1-d2 and 4,4,4-d3 isotopologues of n-butanol suggest the presence of yet unexplored pathways to acetaldehyde.

Kinetics of Several Oxygenated Carbon-Centered Free Radical Reactions with NO2

Five oxygenated carbon-centered free radical reactions with nitrogen dioxide (NO2) have been studied in direct time-resolved measurements. Experiments were conducted in a temperature-controlled flow tube reactor coupled to a 193 nm exciplex laser photolysis and a resonance gas lamp photoionization mass spectrometer. Reactions were investigated under pseudofirst-order conditions, with the NO2 concentrations of the experiments in great excess over the initial radical concentrations ([R]0 << [NO2]). The study consists of the three isomeric C2H5O radicals (CH3CHOH, CH2CH2OH, and CH3OCH2), and the CH2OH and CH3CO radical reactions with NO2 and, hence, includes the three smallest hydroxyalkyl radical species (CH2OH, CH2CH2OH, and CH3CHOH). The obtained rate coefficients are high with the temperature-dependent rate coefficients given by a formula k(T) = k300K × (T/300 K)(-n) as (in units of cm(3) molecule(-1) s(-1)): k(CH2OH + NO2) = (8.95 ± 2.70) × 10(-11) × (T/300 K)(-0.54±0.27) (T = 298-363 K), k(CH2CH2OH + NO2) = (5.99 ± 1.80) × 10(-11) × (T/300 K)(-1.49±0.45)(T = 241-363 K), k(CH3CHOH + NO2) = (7.48 ± 2.24) × 10(-11) × (T/300 K)(-1.36±0.41) (T = 266-363 K), k(CH3OCH2 + NO2) = (7.85 ± 2.36) × 10(-11) × (T/300 K)(-0.93±0.28) (T = 243-363 K), and k(CH3CO + NO2) = (2.87 ± 0.57) × 10(-11) × (T/300 K)(-2.45±0.49) (T = 241-363 K), where the uncertainties refer to the estimated overall uncertainties of the values obtained. The determined rate coefficients show negative temperature dependence with no apparent bath gas pressure dependence under the current experimental conditions (241-363 K and about 1-3 Torr helium). This behavior is typical for a radical-radical addition mechanism with no potential energy barrier above the energy of the separated reactants in the entrance channel of the reaction. Unfortunately the absence of detected product signals prevented gaining deeper insight into the reaction mechanism.

Reactions of Hydrocarbon Radicals and Biradicals

Experimental measurements of the rate coefficients for several types of gas phase radical reactions are reviewed. They include radical isomerization and dissociation, radical + radical association, and unimolecular reactions of peroxy radicals. Some reactions of methylene in its lowest singlet state are also considered. The links to theories of chemical reaction rates and especially of capture rates for radical + radical reactions are examined. Many of the reactions involve formation of adducts, which can isomerize and dissociate. Such reactions frequently involve energy distributions of the adducts that are far from Boltzmann, and the interpretation of measurements requires the use of master equation techniques. The basis of these methods and the use of matrix diagonalization and eigenvector/eigenvalue analysis to extract phenomenological rate coefficients are discussed. The relevance of the measurements to applications in atmospheric chemistry and, especially, in combustion is briefly considered.

Size Effects on Cation Heats of Formation. II. Methyl Substitutions in Oxygen Compounds

A relation between the heat of formation of molecular ions and cation size is used to study the effects of methyl substitution on a series of species containing oxygen. These include methanol, the hydroxymethyl radical, formaldehyde and related isomers, acetaldehyde and related isomers, ketene, formic acid, and acetic acid. This size-dependent relation is found to be valid in most cases, enabling a choice to be made among conflicting reported ion and neutral heat of formation values, but it holds much less well in methyl-substituted formaldehyde and its carbene isomers. The cations formed in methanol, hydroxymethyl, hydroxycarbene, and formic acid by methyl substitution at carbon sites were found to be more stable than those substituted at oxygen sites. Suggestions are made for investigating or reinvestigating the ionization energies and the heats of formation of several of the molecules studied in cases where multiple choices are available in the literature or where our analysis suggests that more reliable values are needed.

Spectroscopic Identification of Isomeric Jet-Cooled Benzyl-Type Radicals Generated from 4-Fluoro-o-xylene

Vibronically excited but jet-cooled benzyl-type radicals were generated by the corona discharge of precursor 4-fluoro-o-xylene seeded in a large amount of inert carrier gas helium using a pinhole-type glass nozzle, from which the vibronic emission spectra were observed with a long-path monochromator in the visible region. From an analysis of the spectra observed, we identified the existence of two isomeric benzyl-type radicals, 2-methyl-4-fluorobenzyl and 2-methyl-5-fluorobenzyl radicals in corona discharge, and determined the electronic energy of the D1 → D0 transition and several vibrational mode frequencies in the D0 state of both isomers for the first time.

Directly measuring reaction kinetics of ˙QOOH – a crucial but elusive intermediate in hydrocarbon autoignition

Hydrocarbon autoignition has long been an area of intense fundamental chemical interest, and is a key technological process for emerging clean and efficient combustion strategies. Carbon-centered radicals containing an -OOH group, commonly denoted ˙QOOH radicals, are produced by isomerization of the alkylperoxy radicals that are formed in the first stages of oxidation. These ˙QOOH radicals are among the most critical species for modeling autoignition, as their reactions with O2 are responsible for chain branching below 1000 K. Despite their importance, no ˙QOOH radicals have ever been observed by any means, and only computational and indirect experimental evidence has been available on their reactivity. Here, we directly produce a ˙QOOH radical, 2-hydroperoxy-2-methylprop-1-yl, and experimentally determine rate coefficients for its unimolecular decomposition and its association reaction with O2. The results are supported by high-level theoretical kinetics calculations. Our experimental strategy opens up a new avenue to study the chemistry of ˙QOOH radicals in isolation.

An extensive methodological theoretical study of the kinetics of the benzylperoxy radical isomerization

Theoretical calculations are carried out on benzylperoxy radical four-center isomerization reaction. Geometry optimizations and vibrational frequency calculations are performed using three methods (B3LYP, MPW1K, and MP2) and seven basis sets (6-31G(d,p), 6-31+G(d,p), 6-31++G(d,p), 6-311G(d,p), cc-pVDZ, aug-cc-pVDZ, and cc-pVTZ). Single-point energy calculations are performed with the highly-correlated ab initio coupled cluster method in the space of single, double, and triple (perturbatively) electron excitations (CCSD(T)) using the 6-311G(d,p), 6-311+G(d,p), 6-311++G(d,p), 6-311+G(3df,2p), and cc-pVTZ basis sets, and with the CASPT2/ANO-L-VDZP level of theory. Canonical transition state theory with a Wigner tunneling correction is used to calculate the high-pressure limit rate constant. The rate constants at 773K calculated with the CASPT2/ANO-L-VDZP//B3LYP/cc-pVDZ and CASPT2/ANO-L-VDZP//B3LYP/aug-cc-pVDZ levels of theory are in very good agreement with the literature value from Ellis et al. These levels of theory are then used to compute the temperature dependence of rate constant and leads to the following three-parameter Arrhenius expressions over the range 600–2000K: k (s−1)=1.34×1010T0.79 exp(−133.1kJmol−1/RT) and k (s−1)=1.85×1010T0.78 exp(−133.9kJmol−1/RT) at the CASPT2/ANO-L-VDZP//B3LYP/cc-pVDZ and CASPT2/ANO-L-VDZP//B3LYP/aug-cc-pVDZ levels of theory, respectively. These relations can be used in oxidation thermokinetic models involving toluene and alkylbenzenes.

Kinetics and mechanism of benzyl chloride reaction with zinc in dimethylacetamide

Oxidative dissolution of zinc in the system of benzyl chloride-dimethylacetamide was investigated. The reaction stereochemistry as well as intermediates and reaction products formed were studied. The kinetic and thermodynamic parameters of the process were measured. The process was shown to follow the Langmuir-Hinshelwood mechanism with the formation of benzyl radicals and mono-solvated organozinc compound on the zinc surface. The components of mixture are adsorbed at various sites of the zinc surface, while recombination and the isomerization of the benzyl radicals occurs in solution.

Thermochemistry of radicals formed by hydrogen abstraction from 1-butanol, 2-methyl-1-propanol, and butanal

We calculate the standard state entropy, heat capacity, enthalpy, and Gibbs free energy for 13 radicals important for the combustion chemistry of biofuels. These thermochemical quantities are calculated from recently proposed methods for calculating partition functions of complex molecules by taking into account their multiple conformational structures and torsional anharmonicity. The radicals considered in this study are those obtained by hydrogen abstraction from 1-butanol, 2-methyl-1-propanol, and butanal. Electronic structure calculations for all conformers of the radicals were carried out using both density functional theory and explicitly correlated coupled cluster theory with quasipertubative inclusion of connected triple excitations. The heat capacity and entropy results are compared with sparsely available group additivity data, and trends in enthalpy and free energy as a function of radical center are discussed for the isomeric radicals.

Unexpected observation of carbonyl oxide radical cations from peroxy radical cations. A new isomerism of oxygen‐containing radical cations

DFT computational studies with B3LYP/6‐31G(d) level theory has been carried out for peroxy radical cations which are formed by the reaction of molecular oxygen with aliphatic and aromatic olefin radical cations. The calculations have led us to find rearrangement reactions of the peroxy radical cations to the isomeric carbonyl oxide radical cations. The results show that the peroxy radical cations in which their positive charges at the olefinic carbons cannot be stabilized due to the structural requirements have a great tendency to undergo the rearrangement. Thus, 2‐methylpropene radical cation does not afford a peroxy radical cation formed by the addition of molecular oxygen at 2‐position of the olefinic carbon, and DFT calculations to locate the structure were found to give a rearranged ethyl methyl carbonyl oxide radical cation, which is significantly more stable than the peroxy radical cation. It was also found that carbonyl oxide radical cations, depending on the structures, are as stable as, or even more stable than, the isomeric peroxy radical cations which are formed by the addition of molecular oxygen to the aromatic olefin radical cations derived from trans‐stilbene and β‐methylstyrene. The results also indicate that the C–O bonds are shorter than the O–O bonds in the alkyl carbonyl oxide radical cations examined, which suggests that oxygen lone pair delocalization to the carbonyl carbon play an important role for the determinaton of the structures and their stability. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Mechanism and kinetic study on the gas-phase reactions of OH radical with carbamate insecticide isoprocarb

As one of the most important carbamate insecticides, isoprocarb [2-(1-methylethyl) phenyl methylcarbamate, MIPC] is widely used in agricultural and cotton spraying. The atmospheric chemical reaction mechanism and kinetics of MIPC with OH radical have been researched using the density functional theory in this paper. The study shows that OH radical is more easily added to the C atoms of aromatic ring than to carbon-oxygen double bond, while the H atom is abstracted more difficulty from –CONH– group and aromatic ring than from the –CH3– group and the –CH– group. At room temperature, the total rate constant of MIPC with OH radical is about 5.1 × 10−12 cm3 molecule−l s−l. OH radical addition reaction and H atom abstraction reaction are both important for the OH-initiated reaction of MIPC. The energy-rich adducts (MIPC-OH) and the MIPC's radical isomers are open-shell activated radicals and can be further oxidized in the atmosphere.

The decomposition of 2-pentyl and 3-pentyl radicals

The isomerization and decomposition reactions of 2-pentyl and 3-pentyl radicals have been studied in a single-pulse shock tube over a temperature range of 973–1121K and pressures of 120–800kPa. The results represent the first direct study of the alkene product branching ratio resulting from the kinetics of the competition between isomerization and beta C–C bond scission for a secondary straight-chain alkyl radical at high temperatures. Such species are representative of intermediates important in the combustion of typical hydrocarbon fuels. In the present work, a small quantity of precursor (∼45μL/L) is used to thermally generate H atoms in the presence of excess (E)-2-pentene, leading to the radicals of interest via addition of H to the double bond. Decomposition of the chemically activated pentyl radicals results in the stable olefin products ethene, propene, and 1-butene, which are detected in postshock gas chromatographic analyses utilizing flame-ionization and mass-spectrometric detection. It is shown that the olefin product ratios can be related to the isomerization and decomposition reactions of the 2-pentyl and 3-pentyl radicals and the results are consistent with the existence of distinct non-overlapping cracking patterns for the two radicals. The data are compared with predictions made on the basis of a model developed from experiments on the decomposition of thermal (i.e. not chemically activated) 1-pentyl radicals. Good agreement is observed. In conjunction with an RRKM/Master Equation analysis, the results for 2-pentyl and 3-pentyl radicals are projected over a wide range of temperatures. In addition, the rate constants for addition of H atoms to the alternate double bond positions of (E)-2-pentene are derived relative to a standard reaction and absolute rate constants for these processes are reported.

High molecular weight SOA formation during limonene ozonolysis: insights from ultrahigh-resolution FT-ICR mass spectrometry characterization

Abstract. The detailed molecular composition of laboratory generated limonene ozonolysis secondary organic aerosol (SOA) was studied using ultrahigh-resolution Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Approximately 1200 molecular formulas were identified in the SOA over the mass range of 140 to 850 Da. Four characteristic groups of high relative abundance species were observed; they indicate an array of accretion products that retain a large fraction of the limonene skeleton. The identified molecular formulas of each of the groups are related to one another by CH2, O and CH2O homologous series. The CH2 and O homologous series of the low molecular weight (MW) SOA (m/z &lt; 300) are explained with a combination of functionalization and fragmentation of radical intermediates and reactive uptake of gas-phase carbonyls. They include isomerization and elimination reactions of Criegee radicals, reactions between alkyl peroxy radicals, and scission of alkoxy radicals resulting from the Criegee radicals. The presence of compounds with 10–15 carbon atoms in the first group (e.g. C11H18O6) provides evidence for SOA formation by the reactive uptake of gas-phase carbonyls during limonene ozonolysis. The high MW compounds (m/z &gt; 300) were found to constitute a significant number fraction of the identified SOA components. The formation of high MW compounds was evaluated by molecular formula trends, fragmentation analysis of select high MW compounds and a comprehensive reaction matrix including the identified low MW SOA, hydroperoxides and Criegee radicals as building blocks. Although the formation of high MW SOA may occur via a variety of radical and non-radical reaction channels, the combined approach indicates a greater importance of the non-condensation reactions over aldol and ester condensation reaction channels. Among these hemi-acetal reactions appear to be most dominant followed by hydroperoxide and Criegee reaction channels.

Isomerization kinetics of benzylic and methylphenyl type radicals in single-ring aromatics

Mutual isomerization through H-atom shifts in benzylic and methylphenyl type radicals are examined for toluene, and o-, m-, and p-xylene isomers. In the high temperature pyrolysis and oxidation of toluene, three possible methylphenyl radical isomers can be formed (2-, 3-, and 4-methylphenyl). The 2-methylphenyl radical may undergo a facile isomerization to benzyl through a four-membered ring critical structure – a pathway not accessible to 3- and 4-methylphenyl. Electronic structure calculations show that 2-methylphenyl isomerization to benzyl is preferred energetically by at least 20kcal/mol over other possibilities. Monte Carlo RRKM/master equation simulations illustrate that, at temperatures ⩾1200K, and for almost all pressures, the 2-methylphenyl radical has a lifetime of only several microseconds, whereas 3- and 4-methylphenyl radicals have a substantially longer lifetime, allowing them to react with other species, including molecular oxygen, during toluene oxidation. This is also found to be the case for all dimethylphenyl radicals in the three xylene isomers. As a result, the structure of the xylene isomers and specifically the number of H atoms immediately adjacent to the methyl groups can have a direct impact on their high-temperature oxidation and appear to explain the observed differences in xylene oxidation behind reflected shock waves and in laminar premixed flames.

Kinetics of n-Butoxy and 2-Pentoxy Isomerization and Detection of Primary Products by Infrared Cavity Ringdown Spectroscopy

The primary products of n-butoxy and 2-pentoxy isomerization in the presence and absence of O(2) have been detected using pulsed laser photolysis-cavity ringdown spectroscopy (PLP-CRDS). Alkoxy radicals n-butoxy and 2-pentoxy were generated by photolysis of alkyl nitrite precursors (n-butyl nitrite or 2-pentyl nitrite, respectively), and the isomerization products with and without O(2) were detected by infrared cavity ringdown spectroscopy 20 μs after the photolysis. We report the mid-IR OH stretch (ν(1)) absorption spectra for δ-HO-1-C(4)H(8)•, δ-HO-1-C(4)H(8)OO•, δ-HO-1-C(5)H(10)•, and δ-HO-1-C(5)H(10)OO•. The observed ν(1) bands are similar in position and shape to the related alcohols (n-butanol and 2-pentanol), although the HOROO• absorption is slightly stronger than the HOR• absorption. We determined the rate of isomerization relative to reaction with O(2) for the n-butoxy and 2-pentoxy radicals by measuring the relative ν(1) absorbance of HOROO• as a function of [O(2)]. At 295 K and 670 Torr of N(2) or N(2)/O(2), we found rate constant ratios of k(isom)/k(O(2)) = 1.7 (±0.1) × 10(19) cm(-3) for n-butoxy and k(isom)/k(O(2)) = 3.4(±0.4) × 10(19) cm(-3) for 2-pentoxy (2σ uncertainty). Using currently known rate constants k(O(2)), we estimate isomerization rates of k(isom) = 2.4 (±1.2) × 10(5) s(-1) and k(isom) ≈ 3 × 10(5) s(-1) for n-butoxy and 2-pentoxy radicals, respectively, where the uncertainties are primarily due to uncertainties in k(O(2)). Because isomerization is predicted to be in the high pressure limit at 670 Torr, these relative rates are expected to be the same at atmospheric pressure. Our results include corrections for prompt isomerization of hot nascent alkoxy radicals as well as reaction with background NO and unimolecular alkoxy decomposition. We estimate prompt isomerization yields under our conditions of 4 ± 2% and 5 ± 2% for n-butoxy and 2-pentoxy formed from photolysis of the alkyl nitrites at 351 nm. Our measured relative rate values are in good agreement with and more precise than previous end-product analysis studies conducted on the n-butoxy and 2-pentoxy systems. We show that reactions typically neglected in the analysis of alkoxy relative kinetics (decomposition, recombination with NO, and prompt isomerization) may need to be included to obtain accurate values of k(isom)/k(O(2)).

Atmospheric Fate of Methacrolein. 1. Peroxy Radical Isomerization Following Addition of OH and O2

Peroxy radicals formed by addition of OH and O(2) to the olefinic carbon atoms in methacrolein react with NO to form methacrolein hydroxy nitrate and hydroxyacetone. We observe that the ratio of these two compounds, however, unexpectedly decreases as the lifetime of the peroxy radical increases. We propose that this results from an isomerization involving the 1,4-H-shift of the aldehydic hydrogen atom to the peroxy group. The inferred rate (0.5 ± 0.3 s(-1) at T = 296 K) is consistent with estimates obtained from the potential energy surface determined by high level quantum calculations. The product, a hydroxy hydroperoxy carbonyl radical, decomposes rapidly, producing hydroxyacetone and re-forming OH. Simulations using a global chemical transport model suggest that most of the methacrolein hydroxy peroxy radicals formed in the atmosphere undergo isomerization and decomposition.

The influence of isoprene peroxy radical isomerization mechanisms on ozone simulation with the presence of NOx

Isoprene peroxy radical isomerizations (1,5- and 1,6-H shifts) have recently been proposed as important pathways regenerating and recycling HOx (OH + HO2) in the atmosphere under low-NOx conditions (Peeters et al. Phys. Chem. Chem. Phys. 28: 5935–5939 2009; da Silva et al. Environ. Sci. Technol. 44:250–256 2010). Evaluation and comparison of the isoprene peroxy radical isomerization mechanisms from recent studies have been performed against isoprene-NOx experiments conducted in the UNC dual outdoor smog chambers. Five different kinetic mechanisms were tested in this study, including the original Master Chemical Mechanism (MCM) v3.1; two modified MCM mechanisms both implementing isoprene peroxy radical isomerization reactions but with different rate coefficients; the Carbon Bond 6 (CB6) mechanism; and the ISO-UNC mechanism. Sensitivity analyses of the unsaturated hydroxyperoxy aldehydes (HPALDs) reaction mechanisms under fast isomerization have also been performed. The results indicate that the fast isomerization mechanism and the mechanisms with high OH yields from HPALDs photolysis both significantly enhance HOx estimates with increasing isoprene/NOx ratios. However, O3 predictions, as well the isoprene decay rates are substantially overestimated. Our results suggest that given the current state of our knowledge, it is difficult to improve both HOx levels and maintain reasonable O3 simulations using the Peeters et al. (Peeters et al. Phys. Chem. Chem. Phys. 28: 5935–5939 2009) mechanism.

Improvement of the modeling of the low-temperature oxidation of n-butane: study of the primary reactions.

This paper revisits the primary reactions involved in the oxidation of n-butane from low to intermediate temperatures (550-800 K) including the negative temperature coefficient (NTC) zone. A model that was automatically generated is used as a starting point and a large number of thermochemical and kinetic data are then re-estimated. The kinetic data of the isomerization of alkylperoxy radicals giving (•)QOOH radicals and the subsequent decomposition to give cyclic ethers has been calculated at the CBS-QB3 level of theory. The newly obtained model allows a satisfactory prediction of experimental data recently obtained in a jet-stirred reactor and in rapid compression machines. A considerable improvement of the prediction of the selectivity of cyclic ethers is especially obtained compared to previous models. Linear and global sensitivity analyses have been performed to better understand which reactions are of influence in the NTC zone.

Photolysis, OH reactivity and ozone reactivity of a proxy for isoprene-derived hydroperoxyenals (HPALDs)

The C(5)-hydroperoxyenals (C(5)-HPALDs) are a newly-recognized class of multi-functional hydrocarbons produced during the hydroxyl radical (OH)-initiated oxidation of isoprene. Recent theoretical calculations suggest that fast photolysis of these compounds may be an important OH source in high-isoprene, low-NO regions. We report experimental constraints for key parameters of photolysis, OH reaction and ozone reaction of these compounds as derived from a closely-related, custom-synthesized C(6)-HPALD. The photolysis quantum yield is 1.0 ± 0.4 over the range 300-400 nm, assuming an absorption cross section equal to the average of those measured for several analogous enals. The yield of OH from photolysis was determined as 1.0 ± 0.8. The OH reaction rate constant is (5.1 ± 1.8) × 10(-11) cm(3) molecule(-1) s(-1) at 296 K. The ozone reaction rate constant is (1.2 ± 0.2) × 10(-18) cm(3) molecule(-1) s(-1) at 296 K. These results are consistent with previous first-principles estimates, though the nature and fate of secondary oxidation products remains uncertain. Incorporation of C(5)-HPALD chemistry with the above parameters in a 0-D box model, along with experimentally-constrained rates for C(5)-HPALD production from isomerization of first-generation isoprene hydroxyperoxy radicals, is found to enhance modeled OH concentrations by 5-16% relative to the traditional isoprene oxidation mechanism for the chemical regimes of recent observational studies in rural and remote regions. This enhancement in OH will increase if C(5)-HPALD photo-oxidation products also photolyze to yield additional OH or if the C(5)-HPALD production rate is faster than has been observed.