Kinetics of the gas-phase reactions of Cl atom with selected C2-C5 unsaturated hydrocarbons at 283 &lt;T &lt; 323 K

Wang

Phys. Chem. Chem. Phys.

et al. 2002

117

Chlorine atoms are important oxidants at dawn in the marine boundary layer where a variety of organics are also present, including alkenes. Using the relative rate technique, the kinetics of the gas phase reactions of atomic chlorine with a series of alkenes, relative to n-heptane as a reference, have been investigated at (298 AE 3) K and 1 atmosphere in either synthetic air or nitrogen. The rate constant for n-heptane, relative to n-butane whose rate constant was taken to be 2.18 Â 10 À10 cm 3 molecule À1 s À1, was also measured and found to be (3.97 AE 0.27) Â 10 À10 cm 3 molecule À1 s À1 (2s). Based on this value for the n-heptane reaction, the following absolute values for the rate constants, k (in units of 10 À10 cm 3 molecule À1 s À1) for the chlorine atom reactions were determined: propene, 2.64 AE 0.21; isobutene, 3.40 AE 0.28; 1-butene, 3.38 AE 0.48; cis-2-butene, 3.76 AE 0.84; trans-2-butene, 3.31 AE 0.47; 2-methyl-1-butene, 3.58 AE 0.40; 2-methyl-2-butene, 3.95 AE 0.32; 3-methyl-1-butene, 3.29 AE 0.36; 2-ethyl-1-butene, 3.89 AE 0.41; 1-pentene, 3.97 AE 0.36; 3-methyl-1-pentene, 3.85 AE 0.35; and cis-4-methyl-2-pentene, 4.11 AE 0.55 (AE2s). The errors reflect those in our relative rate measurements but do not include the 10% error in the absolute value of the n-butane rate constant upon which these rate constants are ultimately based. A structure-reactivity scheme is presented that assumes that rate constants for addition of chorine atoms to the double bond, as well as that for abstraction of an allylic hydrogen atom, depend upon the degree of alkyl substitution at the double bond and allylic carbons. The surprising result is that the allylic hydrogen atoms react less rapidly with chlorine atoms than the analogous alkyl hydrogens in alkanes. The atmospheric implications for loss of alkenes in the marine boundary layer are discussed.

Section: Resultscontrasting

confidence: 62%

Kinetics of reactions of chlorine atoms with a series of alkenes at 1 atm and 298 K: structure and reactivity

Wang

Phys. Chem. Chem. Phys.

et al. 2002

117

“…However, reactions of Cl atoms with unsaturated hydrocarbons exhibit addition pathways that compete with, or can dominate the direct abstraction pathway. [3][4][5][6][7][8][9] The energized adduct may eliminate HCl under low pressure…”

Section: Introductionmentioning

confidence: 99%

Photoisomerization and Photoinduced Reactions in Liquid CCl₄ and CHCl₃

Abou‐Chahine¹,

Preston²,

Dunning³

et al. 2013

J. Phys. Chem. A

Transient absorption spectroscopy is used to follow the reactive intermediates involved in the first steps in the photochemistry initiated by ultraviolet (266-nm wavelength) excitation of solutions of 1,5-hexadiene, isoprene and 2,3-dimethylbut-2-ene in carbon tetrachloride or chloroform. Ultraviolet and visible bands centred close to 330 nm and 500 nm in both solvents are assigned respectively to a charge transfer band of Cl-solvent complexes, and the strong absorption band of a higher energy isomeric form of the solvent molecules (iso-CCl3-Cl or iso-CHCl2-Cl). These assignments are supported by calculations of electronic excitation energies. The isomeric forms have significant contributions to their structures from charge-separated resonance forms, and offer a re-interpretation of previous assignments of the carriers of the visible bands that were based on pulsed radiolysis experiments. Kinetic analysis demonstrates that the isomeric forms are produced via the Cl-solvent complexes.Addition of the unsaturated hydrocarbons provides a reactive loss channel for the Cl-solvent complexes, and reaction radii and bimolecular rate coefficients are derived from analysis using a Smoluchowski theory model. For reactions of Cl with 1,5-hexadiene, isoprene and 2,3-dimethylbut-2-ene in CCl4, rate coefficients at 294 K are, respectively, (8.6  0.8)  10 9 M -1 s -1 , (9.5  1.6)  10 9 M -1 s -1 and (1.7  0.1)  10 10 M -1 s -1 . The larger reaction radius and rate coefficient for 2,3-dimethylbut-2-ene are interpreted as evidence for an H-atom abstraction channel that competes effectively with the channel involving addition of a Cl atom to a C=C bond. However, the addition mechanism appears to dominate the reactions of 1,5-hexadiene and isoprene. Two-photon excited CCl4 or CHCl3 can also ionize the diene or alkene solute.

“…The kinetics of the reactions of chlorine atoms with many simple alkenes have been well studied, including ethene, propene, 1-butene, and 1-pentene (Coquet and Ariya, 2000;Ezell et al, 2002;Iyer et al, 1983;Kaiser and Wallington, 1996;Pilgrim et al, 1997;Stutz et al, 1997;Stutz et al, 1998;Wallington et al, 1989;Wallington et al, 1990). In general, these reactions occur via multiple reaction channels.…”

Section: Discussionmentioning

confidence: 99%

“…b Experimental rate constant calculated using literature rate constants and uncertainties for the reference compound (Atkinson and Aschmann, 1985;Coquet and Ariya, 2000;Ezell et al, 2002;Fantechi et al, 1998;Shi and Bernhard, 1997;Smith et al, 2002;Stutz et al, 1998;Wallington et al, 1989) Uncertainty shown is the error of the mean KIE value for compounds with two KIE measurements, and the uncertainty from the standard error of the plot of Equation (1) for compounds with only one KIE measurement. b Iannone et al, (2003) c Mean Cl k value with 1σ standard error of the k values determined using relative rate analysis for compounds measured more than once.…”

mentioning

confidence: 99%

“…q Smith et al, (2002). (Hooshiyar and Niki, 1995) c Shi and Bernhard, (Shi and Bernhard, 1997) d Chatwick et al, (Chadwick et al, 2001) e Anderson et al, (Anderson et al, 2004a) f Anderson et al, (Anderson et al, 2004b) g Atkinson and Arey, (Atkinson and Arey, 2003) 33 (Anderson et al, 2004a;Anderson et al, 2004b;Rudolph et al, 2000), literature Cl-reaction KIE values (Anderson et al, submitted 2006), and literature rate constant data (Aschmann and Atkinson, 1995;Atkinson and Arey, 2003;Atkinson, 1997;Chadwick et al, 2001;Coquet and Ariya, 2000;Hooshiyar and Niki, 1995;Shi and Bernhard, 1997;Stutz et al, 1998;Wallington et al, 1989). b Uncertainties are the standard deviations determined using the reported uncertainties in the literature data and in the KIEs from this work.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Laboratory measurements of the 12C/13C kinetic isotope effects in the gas-phase reactions of unsaturated hydrocarbons with Cl atoms at 298 ± 3 K

et al. 2006

Abstract. The carbon kinetic isotope effects (KIEs) in the reactions of several unsaturated hydrocarbons with chlorine atoms were measured at room temperature and ambient pressure using gas chromatography combustion isotope ratio mass spectrometry (GCC-IRMS). All measured KIEs, defined as the ratio of the rate constants for the unlabeled and labeled hydrocarbon reaction k 12 /k 13 , are greater than unity or normal KIEs.The KIEs, reported in per mil according to Cl ε = (k 12 /k 13 -1) × 1000‰ with the number of experimental determinations in parenthesis, are as follows: ethene, 5.65 ± 0.34 (1);propene, 5.56 ± 0.18 (2); 1-butene, 5. transition state structure. IntroductionThe impact of chlorine atom chemistry on the removal of unsaturated hydrocarbons from the atmosphere has been studied in a significant number of publications (Boudries and Bottenheim, 2000;Jobson et al., 1994;Ramacher et al., 1999;Rudolph et al., 1999;Wingenter et al., 1999). Although reactions with hydroxyl radicals and ozone are far more important on the global scale, particularly in continental mid-latitudes, it is agreed that at high latitudes during Polar Sunrise and in coastal environments in the marine boundary layer, where concentrations of Cl atoms can reach levels of up to 10 5 cm -3 (Chang et al., 2004;Singh et al., 1996), Cl-atom chemistry can significantly increase the removal rate of NMHC from the atmosphere.The usefulness of stable carbon isotope ratio measurements for investigating the OH chemistry of both saturated and unsaturated nonmethane hydrocarbons (NMHC) has been demonstrated recently (Rudolph et al., 2000;Rudolph et al., 2002;Rudolph et al., 2003;Saito et al., 2002;Thompson et al., 2003;Tsunogai et al., 1999). To accurately interpret the isotope ratio measurements of unsaturated hydrocarbons, knowledge of the kinetic isotope fractionations associated with their chemical removal is necessary.Measurements have been reported of the 12 C/ 13 C-KIEs in the reactions of alkenes and aromatic hydrocarbons with OH radicals (Anderson et al., 2004a;Anderson et al., 2004b;Rudolph et al., 2000) and in the reactions of alkenes with ozone (Iannone et al., 2003).To best interpret measurements of NMHC from environments with elevated Cl-atom ExperimentThe method for measuring carbon KIEs for the reactions of NMHC + Cl is similar to the method used for measuring OH-reaction KIEs which has been described in detail in a previous publication . The method required only a few minor changes to generate Cl atoms rather than OH radicals, described recently ( For each experiment, before the Cl-atom reaction was initiated, two or three measurements of the reaction chamber contents were made to verify sufficient stability in both the concentration and stable isotope ratios of the hydrocarbons. From all of the hydrocarbons, the mean relative standard deviation of the individual hydrocarbon concentration measurements was 1.5%, with relative standard deviations ranging from 0.5-3.0%. The mean standard deviation of the stable carbon isotope compositions...