Rate constants for the reaction of OH radicals with a series of alkenes and dialkenes at 295 ± 1 K

Using a relative rate technique, rate constants for the gas phase reactions of the OH radical with n-butane, n-hexane, and a series of alkenes and dialkenes, relative to that for propene, have been determined in one atmosphere of air at 295 ± 1 K. The rate constant ratios obtained were (propene = 1.00): ethene, 0.323 ± 0.014; 1-butene, 1.19 ± 0.06; 1-pentene, 1.19 ± 0.05; 1-hexene, 1.40 ± 0.04; 1-heptene, 1.51 ± 0.06; 3-methyl-1-butene, 1.21 ± 0.04; isobutene, 1.95 ± 0.09; cis-2-butene, 2.13 ± 0.05; trans-2-butene, 2.43 ± 0.05; 2-methyl-2-butene, 3.30 ± 0.13; 2,3-dimethyl-2-butene, 4.17 ± 0.18; propadiene, 0.367 ± 0.036; 1,3-butadiene, 2.53 ± 0.08; 2-methyl-1,3-butadiene, 3.81 ± 0.15; n-butane, 0.101 ± 0.012; and n-hexane, 0.198 ± 0.017. From a least-squares fit of these relative rate data to the most reliable literature absolute flash photolysis rate constants, these relative rate constants can be placed on an absolute basis using a rate constant for the reaction of OH radicals with propene of 2.63 × 10^?11 cm³ molecule^?1 s^?1. The resulting rate constant data, together with previous relative rate data from these and other laboratories, lead to a self-consistent data set for the reactions of OH radicals with a large number of organics at room temperature.     

Rate constants for the gas-phase reactions of O3 with a series of alkenes at 296 ± 2 K

The kinetics of the gas-phase reactions of O₃ with a series of alkenes have been investigated at atmospheric pressure (ca. 740 torr) of air and 296 ± 2 K, using a relative rate method in the presence of sufficient n-octane to scavenge any OH radicals generated in these reactions. Relative to k(O₃ + propene) = 1.00, the rate constants obtained were: 1-butene, 0.975 ± 0.030; 2-methylpropene, 1.14 ± 0.04; 2-methyl-1,3-butadiene (isoprene), 1.21 ± 0.02; 1,4-cyclohexadiene, 4.75 ± 0.23; cyclohexene, 7.38 ± 0.48; cis-2-butene, 12.8 ± 0.8; trans-2-butene, 21.5 ± 1.5; 2-methyl-2-butene, 42.1 ± 2.8; cyclopentene, 64.9 ± 4.3; and 2,3-dimethyl-2-butene, 123 ± 11. These relative rate constants have been placed on an absolute basis using a rate constant for the reaction of O₃ with propene of 1.01 × 10^?17 cm³ molecule^?1 s^?1 at 296 K derived from an analysis of the available literature data. The resulting rate constants then lead to a self-consistent set of room temperature data for the reactions of O₃ with these alkenes. © John Wiley & Sons, Inc.     

Overall rate constant measurements of the reaction of hydroxy- and chloroalkylperoxy radicals derived from methacrolein and methyl vinyl ketone with nitric oxide

The overall rate constants of the reactions of NO with hydroxy- and chloroalkylperoxy radicals, derived from the OH- and Cl-initiated oxidation of methacrolein and methyl vinyl ketone, respectively, were directly determined for the first time using the turbulent-flow technique and pseudo-first-order kinetics conditions with high-pressure chemical ionization mass spectrometry for the direct detection of peroxy radical reactants. The individual 100 Torr, 298 K hydroxyalkylperoxy + NO rate constants for the methacrolein [(0.93 +/- 0.12) (2sigma) x 10(-11) cm3 molecule(-1) s(-1)] and methyl vinyl ketone [(0.84 +/- 0.10) x 10(-11) cm3 molecule(-1) s(-1)] systems were found to be identical within the 95% confidence interval associated with each separate measurement, as were the chloroalkylperoxy + NO rate constants for both methacrolein [(1.17 +/- 0.11) x 10(-11) cm3 molecule(-1) s(-1)] and methyl vinyl ketone [(1.14 +/- 0.14) x 10(-11) cm3 molecule(-1) s(-1)]. However, the difference in the rate constants between the hydroxyperoxy + NO and chloroalkylperoxy + NO systems was found to be statistically significant, with the chloroalkylperoxy + NO rate constants about 30% higher than the corresponding hydroxyalkylperoxy + NO rate constants. This substituent effect was rationalized via a frontier molecular orbital model approach.     

Structure-activity relationship for the addition of OH to (poly)alkenes: site-specific and total rate constants

A novel site-specific structure-activity relationship was developed for the site-specific addition of OH radicals to (poly)alkenes at 298 K. From a detailed structure-activity analysis of some 65 known OH + alkene and diene reactions, it appears that the total rate constant for this reaction class can be closely approximated by a sum of independent partial rate constants, ki, for addition to the specific (double-bonded) C atoms that depend only on the stability type of the ensuing radical (primary, secondary, etc.), that is, on the number of substituents on the neighboring C atom in the double bond. The (nine) independent partial rate constants, ki, were derived, and the predicted rate constants (kOH,pred = Sigmak(i)) were compared with experimental k(OH,exp) values. For noncyclic (poly)alkenes, including conjugated structures, the agreement is excellent (Delta < 10%). The SAR-predicted rate constants for cyclic (poly)alkenes are in general also within <15% of the experimental value. On the basis of this SAR, it is possible to predict the site-specific rate constants for (poly)alkene + OH reactions accurately, including larger biogenic compounds such as isoprene and terpenes. An important section is devoted to the rigorous experimental validation of the SAR predictions against direct measurements of the site-specific addition contributions within the alkene, for monoalkenes as well as conjugated alkenes. The measured site specificities are within 10-15% of the SAR predictions.     

Rate coefficients for the gas-phase reactions of bromine radicals with a series of alkenes,dienes, and aromatic hydrocarbons at 298 ± 2 K

Using the relative kinetic method rate coefficients have been determined for the gas-phase reaction of bromine (Br) radicals with a series of alkenes, chloroalkenes, dienes, and aromatic hydrocarbons in 1000 mbar of synthetic air at 298 ± 2 K. Both the UV photolysis of CH₂Br₂ (λ = 254 nm) and the visible photolysis of Br₂ (320 ≤ λ ≤ 480) were used to generate Br radicals. For the alkenes and dienes the following rate coefficients were obtained (in units of 10⁻¹² cm³ molecule⁻¹ s⁻¹): trans-2-butene 9.26 ± 1.85; 2-methyl-1-butene 15.20 ± 3.00; 2-methyl-2-butene 19.10 ± 3.80; 2,3-dimethyl-2-butene 28.20 ± 5.60; α-pinene 22.20 ± 4.40. β-pinene 28.60 ± 5.70; 1,3-butadiene 57.50 ± 11.50; isoprene 74.20 ± 14.80; and 2,3-dimethyl-1,3-butadiene 81.7 ± 16.30. For the chloroalkenes and aromatic hydrocarbons the following rate coefficients were obtained (in units of 10⁻¹³ cm³ molecule⁻¹ s⁻¹): chloroethene 7.37 ± 1.92; 1,1-dichloroethene 3.66 ± 0.73; trichloroethene 0.90 ± 0.18; tetrachloroethene ≤ 0.1; benzene ≤ 0.10; toluene ≤ 0.10; p-xylene ≤ 0.10; and furan ≤ 0.10. With the exception of trans-2-butene, this study represents the first determination of the rate coefficients for all of the compounds. © 1996 John Wiley & Sons, Inc.     

Rate constants for the reaction of OH radicals with a series of alkanes and alkenes at 299 ± 2 K

Using methyl nitrite photolysis in air as a source of hydroxyl radicals, relative rate constants for the reaction of OH radicals with a series of alkanes and alkenes have been determined at 299 ± 2 K. The rate constant ratios obtained are: relative to n-hexane = 1.00, neopentane 0.135 ± 0.007, n-butane 0.453 ± 0.007, cyclohexane 1.32 ± 0.04; relative to cyclohexane = 1.00, n-butane 0.341 ± 0.002, cyclopentane 0.704 ± 0.007, 2,3-dimethylbutane 0.827 ± 0.004, ethene 1.12 ± 0.05; relative to propene = 1.00, 2-methyl-2-butene 3.43 ± 0.13, isoprene 3.81 ± 0.17, 2,3-dimethyl-2-butene 4.28 ± 0.21. These relative rate constants are placed on an absolute basis using previous absolute rate constant data and are compared and discussed with literature data.     

Peroxy radical isomerization in the oxidation of isoprene

We report experimental evidence for the formation of C(5)-hydroperoxyaldehydes (HPALDs) from 1,6-H-shift isomerizations in peroxy radicals formed from the hydroxyl radical (OH) oxidation of 2-methyl-1,3-butadiene (isoprene). At 295 K, the isomerization rate of isoprene peroxy radicals (ISO2?) relative to the rate of reaction of ISO2? + HO2 is k(isom)(295)/(k(ISO2?+HO2)(295)) = (1.2 ± 0.6) x 10(8) mol cm(-3), or k(isom)(295) ? 0.002 s(-1). The temperature dependence of this rate was determined through experiments conducted at 295, 310 and 318 K and is well described by k(isom)(T)/(k(ISO2?+HO2)(T)) = 2.0 x 10(21) exp(-9000/T) mol cm(-3). The overall uncertainty in the isomerization rate (relative to k(ISO2?+HO2)) is estimated to be 50%. Peroxy radicals from the oxidation of the fully deuterated isoprene analog isomerize at a rate ～15 times slower than non-deuterated isoprene. The fraction of isoprene peroxy radicals reacting by 1,6-H-shift isomerization is estimated to be 8-11% globally, with values up to 20% in tropical regions.     

Formation yields of epoxides and O(3P) atoms from the gas-phase reactions of O3 with a series of alkenes

Reactions of ozone with propene, 1-butene, cis-2-butene, trans-2-butene, 2,3-dimethyl-2-butene, and 1,3-butadiene were carried out in N₂ and air diluent at atmospheric pressure and room temperature and, by monitoring the formation of the epoxides and/or a carbonyl compound formed from the reactions of O(³P) atoms with these alkenes, the formation yields of O(³P) atoms from the O₃ reactions were investigated. No evidence for O(³P) atom formation was obtained, and upper limits to O(³P) atom formation yields of <4% for propene, <5% for 1.3-butadiene, and <2% for the other four alkenes were derived. The reaction of O₃ with 1,3-butadiene led to the direct formation of 3,4-epoxy-1-butene in (2.3 ± 0.4)% yield. These data are in agreement with the majority of the literature data and show that O(³P) atom formation is not a significant pathway in O₃—alkene reactions, and that epoxide formation only occurs to any significant extent from conjugated dienes. © 1994 John Wiley & Sons, Inc.     

Regioselective Condensation of Alkylidenephosphoranes to N-Methoxy- and N-Anilino-1H isoindole-1,3-(2H)-diones

Treatment of 2-methoxyisoindoline-1,3-dione with resonance-stabilized alkylidenephosphoranes afforded the corresponding monoalkenes as the sole reaction product, in ～58–63% yields, whereas more than 80% yields of the same monoolefin products were obtained when the reactions were carried out under microwave conditions. Similarly, 2-(phenylamino)isoindoline-1,3-dione reacted under either thermal or microwave conditions to give only the corresponding monoalkene derivatives. The alkene products from both substrates were further reduced to the corresponding isoindoles using Zn-dust in EtOH. Prediction of the designed compounds and the in vivo anti-inflammation activity of the products in the rat adjuvant model were also studied. The work is the first demonstration of the anti-inflammatory activity of phthalimide derivatives.     

Photooxidation of 1,3-butadiene containing systems: Rate constant determination for the reaction of acrolein with ⋅OH radicals

The photooxidation of the 1,3-butadiene–NO–air system at 298 ± 2 K was investigated in an environmental chamber under simulated atmospheric conditions. The irradiation gave rise to the formation of acrolein in a 55% yield, based on 1,3-butadiene initial concentration for all the experimental runs. The rate of formation of acrolein was the same as that of 1,3-butadiene consumption, indicating that acrolein is the major product of the 1,3-butadiene oxidation in air. The dependence of acrolein concentration on irradiation time showed thata secondary process, identified as an oxidation of acrolein by ^?OH radicals, was occurring during the photochemical runs. The rate constant of this secondary process was determined by measuring the relative rates of disappearance of acrolein and n-butane during the irradiation of acrolein-n-butane-NO-air mixtures. The so obtained relative rate constant value was placed on an absolute basis using a reported rate constant for the n-butane + ^?OH reaction; a value of (1.6 ± 0.2) × 10¹⁰ M^?1 sec^?1 was obtained.     

Kinetics studies of the gas-phase reactions of NO3 radicals with series of 1-alkenes, dienes, cycloalkenes, alkenols, and alkenals

The gas-phase reactions of NO(3) radicals with series of 1-alkenes, dienes, cycloalkenes, alkenols, and alkenals were studied in pure N(2) or 20% O(2)/80% N(2) bath gas at room temperature and atmospheric pressure using a relative rates technique. Rate coefficients were derived from rates of loss of the organic compounds observed using a chemical ionization mass spectrometer. No difference in the measured kinetic data was observed in the presence or absence of O(2). The rate coefficients obtained (k (10(-13) cm(3) molecule(-1) s(-1)), with uncertainties representing 95% confidence intervals) are as follows: 1-hexene, 0.233 ± 0.021; 1-heptene, 0.245 ± 0.029; 1-octene, 0.292 ± 0.044; 1,3-butadiene, 1.24 ± 0.09; isoprene, 6.24 ± 0.11; 2,3-dimethyl-1,3-butadiene, 14.1 ± 0.5; 1,3-cyclohexadiene, 112 ± 8; cyclopentene, 4.82 ± 0.13; cyclohexene, 5.38 ± 0.20; cycloheptene, 5.28 ± 0.23; 2-buten-1-ol (crotyl alcohol), 3.23 ± 0.12; cis-2-penten-1-ol, 3.11 ± 0.11; cis-2-hexen-1-ol, 3.81 ± 0.38; trans-2-pentenal, 0.193 ± 0.040; trans-2-hexenal, 0.136 ± 0.029; trans-2-heptenal, 0.231 ± 0.036; cis-4-heptenal, 4.03 ± 0.24. The measured rate coefficients are compared to values from previous studies and three structure-activity relationships (SARs), and good agreement is found, in general. In particular, the recently developed SAR of Kerdouci et al. (Kerdouci, J.; Picquet-Varrault, B.; Doussin, J. ChemPhysChem2010, 11, 3909-3920.) is found to estimate the rate coefficients within 35% for all of the measured reactions except for NO(3) + 1,3-butadiene. The SAR prediction for that reaction is nearly 50% lower than the measured value, suggesting that it underestimates the effect of conjugation on the reaction of NO(3) with this small diene. The measured rate coefficients for reactions with a series of alkenols are used to modify the SAR substituent factor for the -CH(2)OH group, and those for reactions with a series of trans-2-alkenals are used to derive a substituent factor for the -C(O)H group, which was not included in the original SAR because of insufficient experimental data.     

Rate constants for the gas-phase reaction of ozone with 1, 1-disubstituted alkenes

The gas-phase reaction of ozone with eight alkenes including six 1,1-disubstituted alkenes has been investigated at ambient T (285–298 K) and p = 1 atm. of air. The reaction rate constants are, in units of 10⁻¹⁸ cm³ molecule⁻¹ s⁻¹, 9.50 ± 1.23 for 3-methyl-1-butane, 13.1. ± 1.8 for 2-methyl-1-pentene, 11.3 ± 3.2 for 2-methyl-1,3-butadiene (isoprene), 7.75 ± 1.08 for 2,3,3-trimethyl-1-butene, 3.02 ± 0.52 for 3-methyl-2-isopropyl-1-butene, 3.98 ± 0.43 for 3,4-diethyl-2-hexene, 1.39 ± 17 for 2,4,4-trimethyl-2-pentene, and >370 for (cis + trans)-3,4-dimethyl-3-hexene. For isoprene, results from this study and earlier literature data are consistent with: k (cm³ molecule⁻¹ s⁻¹) = 5.59 (+ 3.51, &minus 2.16) × 10⁻¹⁵ e^{(−3606±279/RT)}, n = 28, and R = 0.930. The reactivity of the other alkenes, six of which have not been studied before, is discussed in terms of alkyl substituent inductive and steric effects. For alkenes (except 1,1-disubstituted alkenes) that bear H, CH₃, and C₂H₅ substituents, reactivity towards ozone is related to the alkene ionization potential: In k<(10⁻¹⁸ cm³ molecule⁻¹ s⁻¹) = (32.89 ± 1.84) − (3.09 ± 0.20) IP (eV), n = 12, and R = 0.979. This relationship overpredicts the reactivity of C_≥3 1-alkenes, of 1,1-disubstituted alkenes, and of alkenes with bulky substituents, for which reactivity towards ozone is lower due to substituent steric effects. The atmospheric persistence of the alkenes studied is briefly discussed. © 1996 John Wiley & Sons, Inc.     

1,2- and 1,4-Diacetoxylation of 1,3-butadiene via 2,5-dihydrothiophene 1,1-dioxide as a probable intermediate

Sulphur dioxide has been found to promote a novel liquid-phase oxidation of 1,3-butadiene in acetic anhydride with oxygen gas and catalytic amounts of concentrated protic acids (e.g. hydrobromic acid). 1,2-Diacetoxy-3-butene and 1,4-diacetoxy-2-butene together with small amounts of 1-hydroxy-2-acetoxy-3-butene and 1-hydroxy-4-acetoxy-2-butene are formed in the reaction.     

Laser-flash photolysis of naphthyl diselenides; reactivities of naphthylseleno radicals

Transient absorption spectra of 1-naphthylseleno (1-NaphSe˙), and 2-naphthylseleno (2-NaphSe˙) radicals, which are generated by laser-flash photolysis of the corresponding diselenides, were observed. The reactions of 1-NaphSe˙, and 2-NaphSe˙ with 2-methyl-1,3-butadiene and α-methylstyrene were investigated by following the decay rates of these seleno radicals. By both steady-state and laser-flash photolysis, it is proved that these seleno radicals add to alkenes in a reversible manner. The reaction rate constants for such reversible addition reactions were determined by conducting the reaction in the presence of O₂, which traps selectively the carbon-centered radicals formed by the addition reaction of the seleno radicals to the alkenes. The reactivity of 2-NaphSe˙ is higher than that of 1-NaphSe˙, both of which are less reactive than PhSe˙. These reactivities were interpreted with the properties of SOMO calculated by MO method. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 193–200, 1998.     

Experimental and ab initio dynamical investigations of the kinetics and intramolecular energy transfer mechanisms for the OH + 1,3-butadiene reaction between 263 and 423 K at low pressure

The rate constants for the reaction of the OH radical with 1,3-butadiene and its deuterated isotopomer has been measured at 1-6 Torr total pressure over the temperature range of 263-423 K using the discharge flow system coupled with resonance fluorescence/laser-induced fluorescence detection of OH. The measured rate constants for the OH + 1,3-butadiene and OH + 1,3-butadiene- d 6 reactions at room temperature were found to be (6.98 +/- 0.28) x 10 (-11) and (6.94 +/- 0.38) x 10 (-11) cm (3) molecule (-1) s (-1), respectively, in good agreement with previous measurements at higher pressures. An Arrhenius expression for this reaction was determined to be k 1 (II)( T) = (7.23 +/- 1.2) x10 (-11)exp[(664 +/- 49)/ T] cm (3) molecule (-1) s (-1) at 263-423 K. The reaction was found to be independent of pressure between 1 and 6 Torr and over the temperature range of 262- 423 K, in contrast to previous results for the OH + isoprene reaction under similar conditions. To help interpret these results, ab initio molecular dynamics results are presented where the intramolecular energy redistribution is analyzed for the product adducts formed in the OH + isoprene and OH + butadiene reactions.     

Formation of O(3P) atoms and epoxides from the gas- phase reaction of O3 with isoprene

The formation yields of 1,2-epoxy-2-methyl-3-butene and 1,2-epoxy-3-methyl-3-butene have been measured from the reaction of O₃ with isoprene at room temperature and one atmosphere total pressure of N₂ and air diluents, with and without cyclohexane to scavenge the OH radicals formed in this reaction system. In addition, a relative rate method was used to determine a rate constant for the gas-phase reaction of O₃ with 1,2-epoxy-2-methyl-3-butene of (2.5 ± 0.7) x 10^-18 cm³ molecules^-1 s^-1 at 296 ± 2 K. Our data show that the epoxide yields in N₂ and air diluents are the same, with formation yields of 1,2-epoxy-2-methyl-3-butene of 0.028 ± 0.007 and of 1,2-epoxy-3-methyl-3-butene of 0.011 ± 0.004. These data further show that the epoxides arise from the primary O₃ reaction with isoprene, and not via the formation of O(³P) atoms from the O₃ - isoprene reaction followed by reaction of these O(³P) atoms with isoprene.     

Computations on the A-X transition of isoprene-OH-O2 peroxy radicals

Calculations are carried out on the A state of HO2, CH3O2, and CH3CH2O2 and 10 isomers and conformers of the isoprene-OH-O2 peroxy radicals derived from OH addition to isoprene (2-methyl-1,3-butadiene). In addition to calculating vertical and adiabatic excitation energies, we consider the effect of excitation on molecular structure, and examine the OO stretching frequencies, which are known to be major features in the absorption spectra of the A states of the smaller radicals. The two methods used are the configuration interaction with single excitations (CIS) method and time-dependent density functional theory (TD-DFT), both with a range of basis sets up to 6-311++G(2df,2pd). TD-DFT overestimates excitation energies considerably, while CIS tends to underestimate them slightly. TD-DFT does seem to capture the trend in excitation energy vs. size for the smaller peroxy radicals. Conformation and configuration strongly affect the excitation energies of the peroxy radicals from isoprene. CIS calculations indicate that the intramolecular OH--O hydrogen bonds, present in the ground state of some peroxy radicals from isoprene, are weakened or broken in the excited state, while TD-DFT calculations suggest they are retained.     

Measurements of the kinetics of the OH‐initiated oxidation of isoprene: Radical propagation in the OH + isoprene + O2 + NO reaction system

The mechanism of the OH‐initiated oxidation of isoprene in the presence of NO and O₂ has been investigated using a discharge‐flow system at 298 K and 2 torr total pressure. OH radical concentration profiles were measured using laser‐induced fluorescence as a function of reaction time. The rate constant for the reaction of OH + isoprene was measured to be (1.10 ± 0.05) × 10⁻¹⁰ cm³ mol⁻¹ s⁻¹. In the presence of NO and O₂, regeneration of OH radicals by the reaction of isoprene‐based peroxy radicals with NO was measured and compared to simulations of the kinetics of this system. The results of these experiments are consistent with an overall rate constant of 9 × 10⁻¹² cm³ mol⁻¹ mol⁻¹ (with an uncertainty factor of 2) for the reaction of isoprene‐based hydroxyalkyl peroxy radicals with NO. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 637–643, 1999     

Effects of ring strain on gas-phase rate constants. 2. OH radical reactions with cycloalkenes

Relative rate constants for the gas-phase reactions of OH radicals with a series of cycloalkenes have been determined at 298 ± 2 K using methyl nitrite photolysis in air as a source of OH radicals. Using a rate constant for the reaction of OH radicals with isoprene of 9.60 × 10^?11 cm³ molecule^?1 s^?1, the rate constants obtained were (X 10¹¹ cm³ molecule^?1 s^?1): cyclopentene 6.39 ± 0.23, cyclohexene 6.43 ± 0.17, cycloheptene 7.08 ± 0.22, 1,3-cyclohexadiene 15.6 ± 0.5, 1,4 cyclohexadiene 9.48 ± 0.39, bicyclo[2.2.1]-2-heptene 4.68 ± 0.39, bicyclo[2.2.1] 2,5 heptadiene 11.4 ± 1.0, and bicyclo[2.2.2] 2 octene 3.88 ± 0.19. These data show that the rate constants for the nonconjugated cycloalkenes studied depend on the number of double bonds and the degree of substitution per double bond, and indicate that there are no obvious effects of ring strain energy on these OH radical addition rate constants. A predictive technique for the estimation of OH radical rate constants for alkenes and cycloalkenes is presented and discussed.     

Atmospheric reaction of OH radicals with 1,3-butadiene and 4-hydroxy-2-butenal

The gas-phase reaction of OH radicals with 1,3-butadiene and 4-hydroxy-2-butenal in the presence of NO has been studied in a flow tube operated at 295 +/- 2 K and pressures of 950 mbar of synthetic air or 100 mbar of an O(2)/He mixture. OH radicals were generated using three different experimental approaches, namely, ozonolysis of tetramethylethylene (dark reaction), photolysis of methyl nitrite, or via the reaction of HO(2) with NO (HO(2) from the reaction of H-atoms with O(2)). Products of the reaction of OH radicals with 1,3-butadiene were HCHO (0.64 +/- 0.08), acrolein (0.59 +/- 0.06), 4-hydroxy-2-butenal (0.23 +/- 0.10), furan (0.046 +/- 0.014), and organic nitrates (0.06 +/- 0.02) accounting for more than 90% of the reacted carbon. There was no significant dependence of product yields on experimental conditions which were varied in a wide range. The formation of the 1,4-addition product 4-hydroxy-2-butenal was confirmed unambiguously for the first time. The rate coefficient k(OH + 4-hydroxy-2-butenal) = (5.1 +/- 0.8) x 10(-11) cm(3) molecule(-1) s(-1) was determined using a relative rate technique (p = 100 mbar, T = 295 +/- 2 K). Products of the reaction of OH radicals with 4-hydroxy-2-butenal were glycolaldehyde (0.40 +/- 0.06), glyoxal (0.17 +/- 0.04), trans-butenedial (0.093 +/- 0.033), and organic nitrates (0.043 +/- 0.015) as well as further carbonylic substances remaining unidentified so far. Corresponding reaction mechanisms describing the formation of the detected products are proposed, and the relevance of these data for atmospheric conditions is discussed.