A consistent model for the thermal decomposition of NCN3 and the singlet– triplet relaxation of NCN

The thermal decomposition of cyanogen azide (NCN₃) and the subsequent collision‐induced intersystem crossing (CIISC) process of cyanonitrene (NCN) have been investigated by monitoring excited electronic state ¹NCN and ground state ³NCN radicals. NCN was generated by the pyrolysis of NCN₃ behind shock waves and by the photolysis of NCN₃ at room temperature. Falloff rate constants of the thermal unimolecular decomposition of NCN₃ in argon have been extracted from ¹NCN concentration–time profiles in the temperature range 617 K <T< 927 K and at two different total densities: k(ρ ≈ 3 × 10^?6 mol/cm³)/s^?1=4.9 × 10⁹ × exp (?71±14 kJ mol^?1/RT) (± 30%); k(ρ ≈ 6 × 10^?6 mol/cm³)/s^?1=7.5 × 10⁹ × exp (‐71±14 kJ mol^?1/RT) (± 30%). In addition, high‐temperature ¹NCN absorption cross sections have been determined in the temperature range 618 K <T< 1231 K and can be expressed by σ /(cm²/mol)= 1.0 × 10⁸ ?6.3 × 10⁴ K^?1 × T (± 50%). Rate constants for the CIISC process have been measured by monitoring ³NCN in the temperature range 701 K <T< 1256 K resulting in k_CIISC (ρ ≈ 1.8 ×10^?6 mol/cm³)/ s^?1=2.6 × 10⁶× exp (‐36±10 kJ mol^?1/RT) (± 20%), k_CIISC (ρ ≈ 3.5×10^?6 mol/cm³)/ s^?1 = 2.0 × 10⁶ × exp (?31±10 kJ mol^?1/RT) (± 20%), k_CIISC (ρ ≈ 7.0×10^?6 mol/cm³)/ s^?1=1.4 × 10⁶ × exp (?25±10 kJ mol^?1/RT) (± 20%). These values are in good agreement with CIISC rate constants extracted from corresponding ¹NCN measurements. The observed nonlinear pressure dependences reveal a pressure saturation effect of the CIISC process. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 30–40, 2013     

Synthesis and Diels-Alder Reactivity of 2,3,5,6-Tetramethylidenenorbornane

Pd-catalyzed double carbomethoxylation of the Diels-Alder adduct of cyclo-pentadiene and maleic anhydride yielded the methyl norbornane-2,3-endo-5, 6-exo-tetracarboxylate ( 4 ) which was transformed in three steps into 2,3,5,6-tetramethyl-idenenorbornane ( 1 ). The cycloaddition of tetracyanoethylene (TCNE) to 1 giving the corresponding monoadduct 7 was 364 times faster (toluene, 25°) than the addition of TCNE to 7 yielding the bis-adduct 9 . Similar reactivity trends were observed for the additions of TCNE to the less reactive 2,3,5,6-tetramethylidene-7-oxanorbornane ( 2 ). The following second order rate constants (toluene, 25°) and activation parameters were obtained for: 1 + TCNE → 7 : k₁ = (255 + 5) 10^?4 mol^?1 · s^?1, ΔH≠ = (12.2 ± 0.5) kcal/mol, ΔS≠ = (?24.8 ± 1.6) eu.; 7 + TCNE → 9 , k₂ = (0.7 ± 0.02) 10^?4 mol^?1 · s^?1, ΔH≠ = (14.1 ± 1.0) kcal/mol, ΔS≠ = ( ?30 ± 3.5) eu.; 2 + TCNE → 8 : k₁ = (1.5 ± 0.03) 10^?4 mol^?1 · s^?1, ΔH≠ = (14.8 ± 0.7) kcal/mol, ΔS≠ = (?26.4 ± 2.3) eu.; 8 + TCNE → 10 ; k₂ = (0.004 ± 0.0002) 10^?4 mol^?1 · s^?1, ΔH≠ = (17 ± 1.5) kcal/mol, ΔS≠ = (?30 ± 4) eu. The possible origins of the relatively large rate ratios k₁/k₂ are discussed briefly.     

Free‐radical copolymerization of styrene and m‐isopropenyl‐α,α′‐dimethylbenzyl isocyanate studied by 1H NMR kinetic experiments

The free‐radical copolymerization of m‐isopropenyl‐α,α′‐dimethylbenzyl isocyanate (TMI) and styrene was studied with ¹H NMR kinetic experiments at 70 °C. Monomer conversion vs time data were used to determine the ratio k_p × k_t^?0.5 for various comonomer mixture compositions (where k_p is the propagation rate coefficient and k_t is the termination rate coefficient). The ratio k_p × k_t^?0.5 varied from 25.9 × 10^?3 L^0.5 mol^?0.5 s^?0.5 for pure styrene to 2.03 × 10^?3 L^0.5 mol^?0.5 s^?0.5 for 73 mol % TMI, indicating a significant decrease in the rate of polymerization with increasing TMI content in the reaction mixture. Traces of the individual monomer conversion versus time were used to map out the comonomer mixture composition drift up to overall monomer conversions of 35%. Within this conversion range, a slight but significant depletion of styrene in the monomer feed was observed. This depletion became more pronounced at higher levels of TMI in the initial comonomer mixture. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1064–1074, 2002     

Interaction of poly(vinyl acetate) radical with iron (III) complexes

The polymerization of vinyl acetate in N,N-dimethylformamide (DMF) at 60°C initiated by AIBN in the presence of [Fe(DMF)₆](ClO₄)₃ and Fe(N₃)₃ had been studied. Fe(N₃)₃ was produced in situ by mixing solid sodium azide (NaN₃) and hexakis(N,N-dimethylformamide) iron (III) perchlorate, [Fe(DMF)₆](ClO₄)₃, in the ratio of 3:1. The velocity constant k_x for the interaction of poly(vinyl acetate) radical with [Fe(DMF)₆]³⁺ was found to be 1.44 × 10³L mol^?1 s^?1 and that for the interaction of poly(vinyl acetate) radical with Fe(N₃)₃ to be 3.44 × 10⁵ L mol^?1 s^?1 at 60°C.     

Relative rates of nucleophilic reactions of benzyl carbocation formed in photolysis of benzyl chloride and benzyl acetate in aqueous solution

Benzyl chloride and benzyl acetate were photolyzed in 30% methanol–water mixtures (V/V) at 0°C. The photolysis produces benzyl carbocations that react with nucleophiles. The reaction products were analyzed by gas chromatography or liquid chromatography. From the amounts of products the relative values of rate constants of reactions of benzyl carbocation with nucleophiles N and water k(N)/k(H₂O) were calculated. Benzyl carbocation reacts with I^?, Br^?, Cl^?, and Ac^? ions with approximately diffusion-controlled rate. A value of 2.4 × 10⁷ dm³ mol^?1 s^?1 for the rate constant k(H₂O) and a lifetime of 0.7 ns were estimated for benzyl carbocation in the aqueous solution.     

氢过碘酸）合银（III）配离子氧化L-脯氨酸的反应动力学及机理

L-脯氨酸独有的亚胺基使其在生物医药领域具有许多独特的功能,并广泛用作不对称有机化合物合成的有效催化剂。本文在碱性介质中研究了二（氢过碘酸）合银（III）配离子氧化 L-脯氨酸的反应。经质谱鉴定,脯氨酸氧化后的产物为脯氨酸脱羧生成的 γ-氨基丁酸盐;氧化反应对脯氨酸及Ag(III) 均为一级;二级速率常数 k′ 随 [IO₄^-] 浓度增加而减小,而与 [OHˉ] 的浓度几乎无关;推测反应机理应包括 [Ag(HIO₆)₂]^5-与 [Ag(HIO₆)(H₂O)(OH)]^2-之间的前期平衡,两种Ag（III）配离子均作为反应的活性组分,在速控步被完全去质子化的脯氨酸平行地还原,两速控步对应的活化参数为： k₁ (25 ^oC)＝1.87±0.04（mol·L^-1)^-1s^-1,∆ H₁^≠＝45±4 kJ · mol^-1, ∆ S₁^≠＝-90±13 J· K^-1·mol^-1 and k₂ (25 ^oC) ＝3.2±0.5（mol·L^-1)^-1s^-1, ∆ H₂^≠＝34±2 kJ · mol^-1, ∆ S₂^≠＝-122 ±10 J· K^-1·mol^-1。本文第一次发现 [Ag(HIO₆)₂]^5-配离子也具有氧化反应活性。     

Initiator efficiency of 2,2′‐azobis(isobutyronitrile) in bulk dodecyl acrylate free‐radical polymerizations over a wide conversion and molecular weight range

An Erratum has been published for this article in J. Polym. Sci. Part A: Polym. Chem. (2004) 42(21) 5559 . The initiator efficiency, f, of 2,2′‐azobis(isobutyronitrile) (AIBN) in dodecyl acrylate (DA) bulk free‐radical polymerizations has been determined over a wide range of monomer conversion in high‐molecular‐weight regimes (M_n ? 10⁶ g mol^?1 [? 4160 units of DA)] with time‐dependent conversion data obtained via online Fourier transform near infrared spectroscopy (FTNIR) at 60 °C. In addition, the required initiator decomposition rate coefficient, k_d, was determined via online UV spectrometry and was found to be 8.4 · 10^?6 s^?1 (±0.5 · 10^?6 s^?1) in dodecane, n‐butyl acetate, and n‐dodecyl acetate at 60 °C. The initiator efficiency at low monomer conversions is relatively low (f = 0.13) and decreases with increasing monomer to polymer conversions. The evolution of f with monomer conversion (in high‐molecular‐weight regimes), x, at 60 °C can be summarized by the following functionality: f^{60 °C} (x) = 0.13–0.22 · x + 0.25 · x² (for x ≤ 0.45). The reported efficiency data are believed to have an error of >50%. The ratio of the initiator efficiency and the average termination rate coefficient, 〈k_t±, (f/〈k_t〉) has been determined at various molecular weights for the generated polydodecyl acrylate (M_n = 1900 g mol^?1 (? 8 units of DA) up to M_n = 36,500 g mol^?1 (? 152 units of DA). The (f/〈k_t〉) data may be indicative of a chain length‐dependent termination rate coefficient decreasing with (average) chain length. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5170–5179, 2004     

Controlled radical polymerization of styrene mediated by the C‐phenyl‐N‐tert‐butylnitrone/AIBN pair: Kinetics and electron spin resonance analysis

Kinetics of the free radical polymerization of styrene at 110 °C has been investigated in the presence of C‐phenyl‐N‐tert‐butylnitrone (PBN) and 2,2′‐azobis(isobutyronitrile) (AIBN) after prereaction in toluene at 85 °C. The effect of the prereaction time and the PBN/AIBN molar ratio on the in situ formation of nitroxides and alkoxyamines (at 85 °C), and ultimately on the control of the styrene polymerization at 110 °C, has been investigated. As a rule, the styrene radical polymerization is controlled, and the mechanism is one of the classical nitroxide‐mediated polymerization. Only one type of nitroxide (low‐molecular‐mass nitroxide) is formed whatever the prereaction conditions at 85 °C, and the equilibrium constant (K) between active and dormant species is 8.7 × 10^?10 mol L^?1 at 110 °C. At this temperature, the dissociation rate constant (k_d) is 3.7 × 10^?3 s^?1, the recombination rate constant (k_c) is 4.3 × 10⁶ L mol^?1 s^?1, whereas the activation energy (E_a,diss.), for the dissociation of the alkoxyamine at the chain‐end is ～125 kJ mol^?1. Importantly, the propagation rate at 110 °C, which does not change significantly with the prereaction time and the PBN/AIBN molar ratio at 85 °C, is higher than that for the thermal polymerization at 110 °C. This propagation rate directly depends on the equilibrium constant K and on the alkoxyamine and nitroxide concentrations, as well. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1219–1235, 2007     

Kinetics and mechanism of the oxidation of iron(II) ion by chlorine dioxide in aqueous solution

The mechanism by which an excess of iron(II) ion reacts with aqueous chlorine dioxide to produce iron(III) ion and chloride ion has been determined. The reaction proceeds via the formation of chlorite ion, which in turn reacts with additional iron(II) to produce the observed products. The first step of the process, the reduction of chlorine dioxide to chlorite ion, is fast compared to the subsequent reduction of chlorite by iron(II). The overall stoichiometry is The rate is independent of pH over the range from 3.5 to 7.5, but the reaction is assisted by the presence of acetate ion. Thus the rate law is given by At an ionic strength of 2.0 M and at 25°C, k_u = (3.9 ± 0.1) × 10³ L mol^?1 s^?1 and k_c = (6 ± 1) × 10⁴ L mol^?1 s^?1. The formation constant for the acetatoiron(II) complex, K_f, at an ionic strength of 2.0 M and 25°C was found to be (4.8 ± 0.8) × 10^?2 L mol^?1. The activation parameters for the reaction were determined and compared to those for iron(II) ion reacting directly with chlorite ion. At 0.1 M ionic strength, the activation parameters for the two reactions were found to be identical within experimental error. The values of ΔH? and ΔS? are 64 ± 3 kJ mol^?1 and + 40 ± 10 J K^?1 mol^?1 respectively. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 554–565, 2004     

Trans ligand influence in cobalt(III) Schiff base complexes: Electronic and steric effects on the kinetics of hydrolysis

Rate constants for the hydrolysis (k_h) of six different amines in trans‐[Co((BA)₂en)(amine)₂]ClO₄ complexes (amine = aniline 1a , para‐toluidine 1b , benzylamine 1c (primary amines), pyrrolidine 2a , piperidine 2b , morpholine 2c (secondary amines), and (BA)₂en = Bisbenzoylacetoneethylenediiminato) in mixed methanol/water (1:1) solvent have been determined between 30 and 55°C. The hydrolysis product of 2c , trans‐[Co((BA)₂en)(morpholine)(H₂O)]ClO₄, has been separately prepared and characterized by UV–vis and ¹H NMR spectroscopy. Depending on the nature of the axial amine ligand the limiting first‐order rate constants for the amine hydrolysis at 40°C range from (3.42 ± 0.10) × 10^?5 to (5.32 ± 0.13) × 10^?5 s^?1. At the first glance, a reasonable trend cannot be established between k_h and the basicity or the inductive trans effect of the amine ligands. However, when the complexes are classified into two groups, based on the type of the amine (primary and secondary), the values of k_h correlate well with the basicity or inductive effect of the amine in each group. The observed trend in k_h values for the complexes with primary amines is 1a (5.32 ± 0.13) × 10^?5 s^?1 > 1b (3.51 ± 0.14) × 10^?5 > 1c (1.72 ± 0.03) × 10^?5 (40°C), which is opposite to the amine basicity strength. In the case of the complexes with secondary amines, the observed trend in k_h values is in accord with amine basicity (or inductive trans effect), i.e. 2a (5.02 ± 0.22) × 10^?5 > 2b (4.18 ± 0.10) × 10^?5 > 2c (3.42 ± 0.10) × 10^?5 s^?1 (40°C). © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 387–393, 2002     

Quantum chemical/vRRKM study on the thermal decomposition of cyclopentadiene

Thermal decomposition of cyclopentadiene to c‐C₅H₅ (cyclopentadienyl radical) + H (1) and the reverse bimolecular reaction (?1) are studied quantum‐chemically at the G2M level of theory. The dissociation pathway has been mapped out following the minimum energy path on the potential energy surface (PES) calculated by the density functional UB3LYP/6‐311G(d,p) method. Using isodesmic reaction analysis, the standard enthalpy of formation for c‐C₅H₅ is found to be 62.5 ± 1.3 kcal mol^?1, and the c‐C₅H₅? H bond dissociation energy is estimated as D°₂₉₈(c‐C₅H₅? H) = 82.5 ± 0.9 kcal mol^?1, in excellent agreement with the recent experimental values. Variational rate constants are computed on the basis of a scaled UB3LYP dissociation potential that fits the isodesmic/experimental enthalpy of Reaction (1). At the high pressure limit, k₁^∞ = 1.55 × 10¹⁸ T^?0.8 exp(?42300/T) s^?1 and k_?1^∞ = 2.67 × 10¹⁴ exp(?245/T) cm³ mol^?1 s^?1. The fall‐off effects are evaluated by a weak collision master equation/RRKM analysis. Calculated T, P‐dependent rate constants are in very good agreement with the most reliable experimental measurements. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 139–151 2004     

The elimination kinetics and mechanisms of ethyl piperidine‐3‐carboxylate,ethyl 1‐methylpiperidine‐3‐carboxylate,and ethyl 3‐(piperidin‐1‐yl)propionate in the gas phase

The gas‐phase elimination kinetics of the above‐mentioned compounds were determined in a static reaction system over the temperature range of 369–450.3°C and pressure range of 29–103.5 Torr. The reactions are homogeneous, unimolecular, and obey a first‐order rate law. The rate coefficients are given by the following Arrhenius expressions: ethyl 3‐(piperidin‐1‐yl) propionate, log k₁(s^?1) = (12.79 ± 0.16) ? (199.7 ± 2.0) kJ mol^?1 (2.303 RT)^?1; ethyl 1‐methylpiperidine‐3‐carboxylate, log k₁(s^?1) = (13.07 ± 0.12)–(212.8 ± 1.6) kJ mol^?1 (2.303 RT)^?1; ethyl piperidine‐3‐carboxylate, log k₁(s^?1) = (13.12 ± 0.13) ? (210.4 ± 1.7) kJ mol^?1 (2.303 RT)^?1; and 3‐piperidine carboxylic acid, log k₁(s^?1) = (14.24 ± 0.17) ? (234.4 ± 2.2) kJ mol^?1 (2.303 RT)^?1. The first step of decomposition of these esters is the formation of the corresponding carboxylic acids and ethylene through a concerted six‐membered cyclic transition state type of mechanism. The intermediate β‐amino acids decarboxylate as the α‐amino acids but in terms of a semipolar six‐membered cyclic transition state mechanism. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 106–114, 2006     

Thermal decomposition of chlorofluoromethyl peroxynitrates

The thermal decomposition of CCl₃O₂NO₂,CCl₂FO₂NO₂, and CClF₂O₂NO₂ was studied in a temperature-controlled 420 l reaction chamber using in situ detection of peroxynitrates by long-path IR absorption. The temperature dependence of the unimolecular dissociation rate constants was determined at total pressures of 10 and 800 mbar in nitrogen as buffer gas, and the pressure dependence was measured at 273 K between 10 and 800 mbar. In Troe's notation, the data are represented by the following values for the limiting low and high pressure rate constants k₀/[N₂] and k_∞ and the fall-off curvature parameter F_c (in units of cm³ molecule^?1 s^?1, s^?1): CCl₃O₂NO₂,k₀/[N₂] = 6.3 × 10^?3 exp(?85.1 kJ · mol^?1/RT), k_∞ = 4.8 × 10¹⁶ exp(?98.3 kJ · mol^?1/RT), F_c = 0.22; CCl₂FO₂NO₂, k₀/[N₂] = 1.01× 10^?2 exp(?90.3 kJ · mol^?1/RT), k_∞ = 6.6 × 10¹⁶ exp(?101.8 kJ · mol^?1/RT), F_c = 0.28; and CClF₂O₂NO₂, k₀/[N₂] = 1.80 × 10^?3 exp(?87.3 kJ · mol^?1/RT), k_∞ = 1.60 × 10¹⁶exp(?99.7 kJ · mol^?1/RT), F_c = 0.30. From these dissociation rate constants and recently measured rate constants for the reverse reaction (see Caralp, Lesclaux, Rayez, Rayez, and Forst [19]), bond energies (=ΔH) of 100, 103, and 104 kJ/mol were derived for the RO₂–NO₂ bonds in CCl₃O₂NO₂, CCl₂FO₂NO₂, and CClF₂O₂NO₂, respectively. The kinetic and thermochemical parameters of these decomposition reactions are compared with those of the dissociation of other peroxynitrates. Atmospheric implications of the thermal stability of chlorofluoromethyl peroxynitrates are briefly discussed.     

Autoxidation of NO in aqueous solution

The reaction of NO with O₂ has been investigated in aqueous solution. As demonstrated by ion chromatography, the sole product is NO₂^?. Kinetic studies of the reaction by stopped-flow methods with absorbance and conductivity detection are in agreement that the rate law is -d[O₂]/dt=k[NO]²[O₂] with k = 2.1 × 10⁶ M^?2 s^?1 at 25°C. This rate law is unaffected by pH over the range from pH 1 to 13, and it holds with either NO or O₂ in excess. By studying the reaction over the temperature range from 10 to 40°C, the following activation parameters were obtained: ΔH^≠ = 4.6 ± 2.1 kJ mol^?1 and ΔS^≠=?96 plusmn; 4 J K^?1 mol^?1. © 1993 John Wiley & Sons, Inc.     

The gas-phase elimination kinetics of 3-buten-1-methanesulphonate and 3-methyl-3-buten-1-methanesulphonate

The elimination kinetics of the title compounds were carried out in a static system over the temperature range of 290–330°C and pressure range of 29.5–124 torr. The reactions, carried out in seasoned vessels with allyl bromide, obey first-order rate law, are homogeneous and unimolecular. The temperature dependence of the rate coefficients is given by the following Arrhenius equations: for 3-buten-1-methanesulphonate, log k₁(s^?1) = (12.95 ± 0.53) ? (175.3 ± 5.9)kJ mol^?1(2.303RT)^?1; and for 3-methyl-3-buten-1-methanesulphonate, log k₁(s^?1) = (12.98 ± 0.40) ? (174.7 ± 4.5)kJ mol^?1(2.303RT)^?1. The olefinic double bond appears to assist in the rate of pyrolysis. The mechanism is described in terms of an intimate ion-pair intermediate. © 1995 John Wiley & Sons, Inc.     

Kinetics of the gas‐phase reactions of chlorine atoms with CH2F2, CH3CCl3, and CF3CFH2 over the temperature range 253–553 K

Relative rate techniques were used to study the title reactions in 930–1200 mbar of N₂ diluent. The reaction rate coefficients measured in the present work are summarized by the expressions k(Cl + CH₂F₂) = 1.19 × 10^?17 T² exp(?1023/T) cm³ molecule^?1 s^?1 (253–553 K), k(Cl + CH₃CCl₃) = 2.41 × 10^?12 exp(?1630/T) cm³ molecule^?1 s^?1 (253–313 K), and k(Cl + CF₃CFH₂) = 1.27 × 10^?12 exp(?2019/T) cm³ molecule^?1 s^?1 (253–313 K). Results are discussed with respect to the literature data. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 401–406, 2009     

Studies on polymerization of vinyl acetate using ylide as an initiator and degradative transfer agent

The polymerization of vinyl acetate initiated by β-picolinium-p-chlorophenacylide was carried out at 30, 35, and 40°C, using the conventional dilatometric technique. The initiator and the monomer exponent values were 0.80 ± 0.15 and unity, respectively. The polymerization was inhibited in the presence of hydroquinone, but was favored by nonpolar solvent and polymerization temperature. The energy of activation was 90.3 kJ mol^?1. An average value of k/k_t for the present system was found to be 0.37 × 10^?2 L mol^?1 s^?1. The results are explained in terms of radical mode of polymerization with degradative initiator transfer; the principal mode of termination, however, was biomolecular.     

Steric influence in the direction of elimination of gas-phase pyrolyses of several highly branched secondary acetates

The rate coefficients for the gas-phase pyrolyses of a series of structurally related secondary acetates have been measured in a static system over the temperature range of 289.1–359.5°C and the pressure range 50.0–203.0 torr. The temperature dependence of the rate coefficients is given by the following Arrhenius equations: for 3-hexyl acetate, log k₁ (s^?) = (12.12 ± 0.33) ? (176.1 ± 3.9)kJ/mol/2.203RT; for 5-methyl-3-hexyl acetate, log k₁ (s^?) = (13.17 ± 0.20) ? (186.2 ± 2.3)kJ/mol/2.303RT; and for 5,5-dimethyl-3-hexyl acetate, log k₁ (s^?) = (12.70 ± 0.19) ? (177.4 ± 2.2)kJ/mol/2.303RT. The direction of elimination of these esters has shown from the invariability of olefin distributions at different temperatures and percentages of decomposition that steric hindrance is a determining factor in the eclipsed cis conformation. Moreover, a more detailed analysis indicates that the greater the alkyl–alkyl interaction, the less favored the elimination tends to be. Otherwise, an increase of alkyl–hydrogen interaction caused steric acceleration to be the determining factor.     

Formation of NO from N2/O2 Mixtures in a Flow Reactor: Toward an Accurate Prediction of Thermal NO

We have conducted flow reactor experiments for NO formation from N₂/O₂ mixtures at high temperatures and atmospheric pressure, controlling accurately temperature and reaction time. Under these conditions, atomic oxygen equilibrates rapidly with O₂. The experimental results were interpreted by a detailed chemical model to determine the rate constant for the reaction N₂ + O ? NO + N (R1). We obtain k₁ = 1.4 × 10¹⁴ exp(?38,300/T) cm³ mol^?1 s^?1 at 1700–1800 K, with an error limit of ±30%. This value is 25% below the recommendation of Baulch et al. for k₁, while it corresponds to a value k_1b of the reverse reaction 25% above the Baulch et al. evaluation. Combination of our results with literature values leads to a recommended rate constant for k_1b of 9.4 × 10¹² T^0.14 cm³ mol^?1 s^?1 over 250–3000 K. This value, which reconciles the differences between the forward and reverse rate constant, is recommended for use in kinetic modeling.     

Measurements of the bimolecular rate constants for S + O2 → SO + O and CS2 + O2 → CS + SO2 at high temperatures

The bimolecular reactions in the title were measured behind shock waves by monitoring the O-atom production in COS? O₂? Ar and CS₂? O₂? Ar mixtures over the temperature range between 1400 and 2200 K. A value of the rate constant for S + O₂ → SO + O was evaluated to be (3.8 ± 0.7) × 10¹² cm³ mol^?1 s^?1 between 1900 and 2200 K. This was connected with the data at lower temperatures to give an expression k₂ = 10^10.85 T^0.52 cm³ mol^?1 s^?1 between 250 and 2200 K. An expression of the rate constant for CS₂ + O₂ → CS + SO₂ was obtained to be k₂₁ = 10^12.0 exp(?32 kcal mol^?1/RT) cm³ mol^?1 s^?1 with an error factor of 2 between 1500 and 2100 K.