Library

Notes: 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.

Notes: The kinetics of the oxidation of lactic and atrolactic acids by ceric sulfate have been studied in the medium HClO4-Na2SO4-NaClO4 at 25.0°C and ionic strength 2.0 mol dm-3 over a wide range of organic substrate (HL), hydrogen and bisulfate ion concentrations. The redox reactions proceed significantly through three simultaneous paths involving intermediate complexes between the reactive cerium(IV) species and the organic substrate according to the following expression \documentclass{article}\pagestyle{empty}\begin{document}$$k_{{\rm obs}} = \frac{{(b[{\rm HSO}_4^ -] + c[{\rm HSO}_4^ -]^2 + [{\rm H}^ +]){\rm [HL]}}}{{\{ f_1 [{\rm HSO}_4^ -]^3 + d_1 [{\rm HSO}_4^ -] + e_1 [{\rm HSO}_4^ -]^2){\rm }[{\rm H}^ +]\} + A'[{\rm HL}]}}$$\end{document} where kobs indicates the observed pseudo-first-order rate constant, b and c are rate constants relative to that for the path associated with the term [H+] in the numerator, and A' is a quantity depending on the [H+] and [HSO4-] concentrations. Moreover, three equilibria involving cerium(IV) and HSO4- (or SO42-) ions are important from a kinetic point of view, the cumulative equilibrium constants being in the ratios β1: β2: β3 = d1: e1: f1. The present data are compared with those obtained previously for the cerium(IV) oxidation of glycolic acid and the substituent effects discussed.

Notes: A kinetic study of oxidation of hydroxylamine by bromate ion in acid sulfate solution using spectrophotometric and potentiometric methods is reported. Oxidation of hydroxylamine to nitrate is quantitative and followed competitive, consecutive, and auto catalytics steps characterized by induction periods. In the slow rate limiting step, hydroxylamine on reaction with HOBr (k1′) forms an intermediate I, which further reacts fast with second molecule of HOBr (k2′) giving nitrite. Nitrite reacts with HOBr (k3′) yielding the final product nitrate. Nitric acts as an autocatalyst also and its initial addition decreased the induction periods. In excess of hydrogen ion concentration all the reaction steps follow second-order kinetics. All the second-order rate constants are reported and the reaction mechanism is proposed.

Notes: The kinetics of OH reactions with 1-4 carbon aliphatic thiols have been investigated over the temperature range 252-430 K. OH radicals were produced by flash photolysis of water vapor at λ 〉 165 nm and detected by time-resolved resonance fluorescence spectroscopy. All thiols investigated react with OH at nearly the same rate; k(298 K) = 3.2-4.6 × 10-11 cm3 molecule-1 s-1, -Eact = 0.6-1.0 kcal/mol, A = 0.6-1.2 × 10-11 cm3 molecule-1 s-1. CH3SH and CH3SD react with OH at identical rates over the entire temperature range investigated. We conclude that the dominant reaction pathway is addition to the sulfur atom.

Notes: A new reaction mechanism describing the atmospheric photochemical oxidation of toluene is formulated and tested against environmental chamber data from the University of California, Riverside, Statewide Air Pollution Research Center (SAPRC). On simulations of toluene - NOx and toluene - benzaldehyde - NOx irradiations, the average predicted O3 and PAN maxima are within 3% of the experimental values. Simulations performed with the new mechanism are used to investigate various mechanistic paths, and to gain insight into areas where our understanding is not complete. Specific areas that are investigated include benzaldehyde photolysis, organic nitrate formation, alternate ring fragmentation pathways, and conjugated γ-dicarbonyl condensation to the aerosol phase.

Notes: The kinetics of the reactions of iron(III) with diglycolic, tartaric, and citric acids have been studied in aqueous acid solutions by the temperature-jump method at 25.0°C and at ionic strengths 1.0 (for tartaric and citric acids) and 0.50 mol/dm3 (for diglycolic acid). The experimental data indicate that iron(III) monochelate formation occurs by the same reaction mechanism for all three ligands examined and that only pathways involving the FeOH2+ ion contribute to the chelation process. The reacting species for citric acid is the undissociated ligand. For tartaric and diglycolic acids both the neutral ligands and the corresponding monoanions react significantly under the experimental conditions used. Kinetic evidence for the contribution of intermediate steps to the limiting rate in the overall chelate-formation process has been obtained and discussed.

Notes: The homogeneous gas-phase decomposition kinetics of methylsilane and methylsilane-d3 have been investigated by the comparative-rate-single-pulse shock-tube technique at total pressures of 4700 torr in the 1125-1250 K temperature range. Three primary processes occur: CH3SiH3 → CH3SiH + H2 (1), CH3SiH3 → CH4 + SiH2 (2), and CH3SiH3 → CH2 = SiH2 + H2 (3). The high-pressure rate constants for the primary processes in CH3SiH3 obtained by RRKM calculations are log (k1 + k3) (s-1) = 15.2 - 64,780 Cal/θ and log k2 (s-) = 14.50 - 67,600 → 2800 Cal/θ. For CH3SiD3 these same rate constants are log k1 (s-) = 14.99 - 64,700 cal/θ log k2 (s-) = 14.68 - 66,700 → 2000 cal/θ, and log k3 (s-) = 14.3 - 64,700 cal/θ.

Notes: Vinylacetylene was pyrolyzed at 300-450°C in a packed and an unpacked static reactor with a pinhole bleed to a quadrupole mass spectrometer. The reactant and C8H8 products were monitored continuously during a reaction by mass spectrometry. In some runs, the products were also analyzed by gas chromatography after the run. In these runs CH4, C2H6, C3H6, and C2H4 were also detected.The reaction for vinylacetylene removal and C8H8 formation is homogeneous, second order in reactant, and independent of the presence of a large excess of N2 or He. However, C8H8 formation is about half-suppressed by the addition of the free-radical scavengers NO or O2. The rate coefficient for total vinylacetylene removal is 1.7 × 106 exp(-79 ± 13 kJ/mol RT) L/mol · s. The major reaction for C4H4 removal is polymerization. In addition four C8H8 isomers, carbon, and small hydrocarbons are formed. The three major C8H8 isomers are styrene, cyclooctatetraene (COT), and 1,5—dihydropentalene (DHP).The C8H8 compounds are formed by both molecular and free-radical processes in a second-order process with an overall k ≃ 3 × 108 exp(-122 kJ/mol RT) L/mol · s (average of packed and unpacked cell results). The molecular process occurs with an overall k = 8.5 × 107 exp (-118 kJ/mol RT) L/mol · s. The COT, DHP, and an unidentified isomer (d), are formed exclusively in molecular processes with respective rate coefficients of 4.4 × 104 exp(-77 kJ/mol RT), 1.7 × 105 exp(-89 kJ/mol RT), and 3.1 × 109 exp(- 148 kJ/mol RT) L/mol · s. The styrene is formed both by a direct free-radical process and by isomerization of COT.

Notes: The reactions where Y = CH3 (M), C2H5 (E), i—C3H7 (I), and t—C4H9 (T) have been studied between 488 and 606 K. The pressures of CHD ranged from 16 to 124 torr and those of YE from 57 to 625 torr. These reactions are homogeneous and first order with respect to each reagent. The rate constants (in L/mol·s) are given by \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm NMBO}} = - {{\left( {26530 \pm 80} \right)} \mathord{\left/ {\vphantom {{\left( {26530 \pm 80} \right)} {4.576T + \left( {6.05 \pm 0.03} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {6.05 \pm 0.03} \right)}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm XMBO}} = - {{\left( {28910 \pm 130} \right)} \mathord{\left/ {\vphantom {{\left( {28910 \pm 130} \right)} {4.576T + \left( {6.32 \pm 0.05} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {6.32 \pm 0.05} \right)}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm NEBO}} = - {{\left( {26150 \pm 120} \right)} \mathord{\left/ {\vphantom {{\left( {26150 \pm 120} \right)} {4.576T + \left( {5.85 \pm 0.05} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {5.85 \pm 0.05} \right)}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm XEBO}} = - {{\left( {28560 \pm 120} \right)} \mathord{\left/ {\vphantom {{\left( {28560 \pm 120} \right)} {4.576T + \left( {6.07 \pm 0.05} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {6.07 \pm 0.05} \right)}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm NIBO}} = - {{\left( {26560 \pm 80} \right)} \mathord{\left/ {\vphantom {{\left( {26560 \pm 80} \right)} {4.576T + \left( {5.57 \pm 0.03} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {5.57 \pm 0.03} \right)}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm XIBO}} = - {{\left( {28350 \pm 100} \right)} \mathord{\left/ {\vphantom {{\left( {28350 \pm 100} \right)} {4.576T + \left( {5.47 \pm 0.04} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {5.47 \pm 0.04} \right)}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm NTBO}} = - {{\left( {28920 \pm 50} \right)} \mathord{\left/ {\vphantom {{\left( {28920 \pm 50} \right)} {4.576T + \left( {5.86 \pm 0.02} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {5.86 \pm 0.02} \right)}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm XTBO}} = - {{\left( {32890 \pm 120} \right)} \mathord{\left/ {\vphantom {{\left( {32890 \pm 120} \right)} {4.576T + \left( {6.19 \pm 0.05} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {6.19 \pm 0.05} \right)}} $$\end{document} The Arrhenius parameters are used as a test for a biradical mechanism and to discuss the endo selectivity of the reactions.

Notes: The rate constants for the quenching of O2(1Δg) with carbon disulfide, dimethyl sulfide, dimethyl disulfide, diallyl disulfide, ethyl mercaptan, and thiophene have been determined in a discharge flow system in the absence of oxygen atoms. The rate constants are found to be (6.5 ± 0.6) × 104, (1.8 ± 0.2) × 104, and (3.5 ± 0.6) × 103 L/mol · s for dimethyl sulfide, ethyl mercaptan, and thiophene, respectively. The other compounds have rate constants 〈9.9 × 102 L/mol · s. In the case of dimethyl sulfide, even when NO2 concentration is more than what is required to remove oxygen atoms completely, the rate constants are found to vary with different amounts of NO2. No correlation is found to exist between the logarithm of the rate constants and the ionization potentials of the compounds.

Notes: The rate of the reaction of aqueous sulfite with the N-chloropeptide N-chloroalanylalanylalanine has been studied as a function of pH, temperature, and ionic strength. The results of this work suggest that the mechanism of the reaction involves the interaction of the neutral chloramine with the three ionic forms of sulfite, SO3-2, HSO3-, and H2SO3, with the rate of reaction increasing rapidly with increasing protonation. The estimated second-order rate constants for each ionic species as a function of temperature are \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {{\rm H}_{\rm 2} {\rm SO}_{\rm 3} } \hfill & {k_1 \, = \,2.00\, \times \,10^8 \,{\rm exp}\left( {{{ - 1544} \mathord{\left/ {\vphantom {{ - 1544} {RT}}} \right. \kern-\nulldelimiterspace} {RT}}} \right){\rm min}^{ - 1} } \hfill \\ {{\rm HSO}_{\rm 3}^ - } \hfill & {k_2 \, = \,4.35\, \times \,10^4 \,{\rm exp}\left( {{{ - 1170} \mathord{\left/ {\vphantom {{ - 1170} {RT}}} \right. \kern-\nulldelimiterspace} {RT}}} \right){\rm min}^{ - 1} } \hfill \\ {\,\,{\rm SO}_{\rm 3}^{ - 2} } \hfill & {k_3 \, = 1.58\, \times \,10^{12} \,{\rm exp}\left( {{{ - 12,660} \mathord{\left/ {\vphantom {{ - 12,660} {RT}}} \right. \kern-\nulldelimiterspace} {RT}}} \right){\rm min}^{ - 1} } \hfill \\ \end{array} $$\end{document} where the activation energies are in units of cal/mol.

Notes: Photochlorination of tetrachloroethylene has been studied in a homogeneous liquid system. Kinetic parameters such as reaction orders for chlorine, tetracholoroethylene and light intensity, preexponential factor, and activation energy were evaluated from experimental data. The following kinetic equation was obtained by parameter estimation following the Marquardt procedure: \documentclass{article}\pagestyle{empty}\begin{document}$$ r = \left( {4.02 \pm 0.46} \right)10^{ - 5} \exp \left( { - \frac{{54,700 \pm 200}}{{RT}}} \right)I^{0.489 \pm 0.003} C_{Cl_2 }^{0.889 \pm 0.160} C_{C_2 Cl_4 }^{1.040 \pm 0.042} $$\end{document}

Notes: The reaction chemistry of C2N2—Ar and C2N2—NO—Ar mixtures has been investigated behind incident shock waves. Progress of the reaction was monitored by observing the cyano radical (CN) in absorption at 388.3 nm. A quantitative spectroscopic model was used to determine concentration histories of CN. From initial slopes of CN concentration during cyanogen pyrolysis, the rate constant for C2N2 + M → 2CN + M (1) was determined to be k1 = (4.11 ± 1.8) × 1016 exp(-47,070 ± 1400/T) cm3/mol · s. A reaction sequence for the C2N2—NO system was developed, and CN profiles were computed. By comparison with experimental CN profiles the rate constant for the reaction CN + NO → NCO + N (3) was determined to be k3 = 10(14.0 ± 0.3) exp(-21,190 ± 1500/T) cm3/mol · s. In addition, the rate of the four-centered reaction CN + NO → N2 + CO (2) was estimated to be approximately three orders of magnitude below collision frequency.

Notes: The general effect of back energy transfer is to reduce the apparent quenching constant which is an important parameter in the interpretation of energy transfer data. However, this interpretation may be erroneous when possible diffusion effects and the existence of nonuniform configurational distributions are not taken into account.

Notes: Diode laser spectroscopy has been employed to monitor the formation of chlorine nitrate (ClONO2) in the association reaction of ClO with NO2. Chlorine nitrate is the only stable end-product of this reaction at room temperature. Time-resolved measurements of ClONO2 formation using molecular modulation showed no evidence for any involvement of unstable isomers of ClNO3 in the reaction. These measurements gave a value of k1 = (1.8 ± 0.4) × 10-31 cm6/molecule2 · s for the reaction \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm ClO}\,\, + \,\,{\rm NO}_{\rm 2} \,\, + \,\,{\rm M}\mathop {\longrightarrow} \limits^{k_1 } {\rm ClONO}_{\rm 2} \,\, + \,\,{\rm M} $$\end{document} at 295 K and an upper limit of 5 ms for the lifetime of any isomeric products at this temperature.

Notes: Chlorocyclopropane has been produced by addition of CH2(1A1) and CH2(3B1) to chloroethene. CH2 was generated by the photolysis of ketene at 313 and 366 nm. Chlorocyclopropane was formed in a chemically activated state, had an energy content between 378 and 427 kJ/mol, and reacted in three parallel channels to 3-chloropropene, cis- and trans-1-chloropropene. As secondary reactions elimination of HCl from the chemically activated primary products occurred to form allene and propyne. The apparent rate constants for the isomerization and elimination reactions are reported. The results of RRKM calculations including distribution functions for the activated chlorocyclopropane and a stepladder model for the deactivation support the proposed reaction scheme.

Notes: The kinetics of OH reactions with furan (k1), thiophene (k2), and tetrahydrothiophene (k3), have been investigated over the temperature range 254-425 K. OH radicals were produced by flash photolysis of water vapor at λ 〉 165 nm and detected by timeresolved resonance fluorescence spectroscopy. The following Arrhenius expressions adequately describe the measured rate constants as a function of temperature (units are cm3 molecule-1 S-1): k1 = (1.33 ± 0.29) × 10-11 exp[(333 ± 67)/T], k2 = (3.20 ± 0.70) × 10-12 exp[(325 ± 71)/T], k3 = (1.13 ± 0.35) × 10-11 exp[(166 ± 97)/T]. The results are compared with previous investigations and their implications regarding reaction mechanisms and atmospheric residence times are discussed.

Notes: The reactions of ground-state S(3PJ) atoms with thiirane, methylthiirane, and trans-2,3-dimethylthiirane have been studied by flash photolysis-VUV kinetic absorption spectroscopy. From the analysis of the S(3PJ) decay plots the following rate constants were determined: (1.4 ± 0.2) × 1013, (2.7 ± 0.3) × 1013 and (4.0 ± 0.2) × 1013 (in cm3 mol-1 s-1 units) for thiirane, methylthiirane and trans-2,3-dimethylthiirane, respectively, showing an upward trend with increasing methylation.

Notes: NO Abstract.

Notes: Kinetics of the basic hydrolysis of 1,2-glyceryl dinitrate (1,2-DNG) and 1,3-glyceryl dinitrate (1,3-DNG) esters were investigated in CO2-free aqueous calcium hydroxide solutions. The hydrolysis reactions were carried out in a temperature controlled reactor vessel with provision for continuous N2 sparging of the reaction mixture. Both glyceryl dinitrate esters hydrolyzed via second-order reaction at 25°C. 1,2-DNG in basic solutions isomerized to 1,3-DNG which subsequently hydrolyzed to yield products. The main hydrolysis product of 1,3-DNG was identified as glycidyl nitrate. Other products formed during the basic hydrolysis of DNGs were nitrites and nitrates.

Notes: From the results of order of magnitude analyses, it is concluded that during the oxidation of toluene, radical-atom and radical-radical reactions (1) and (3) play an unusually important and approximately equal role in the formation of benzaldehyde, an intermediate that leads eventually to the complete removal of the side chain. An additional radical-radical system, reaction (2), is shown to be the most likely source of benzyl alcohol observed during toluene oxidation.

Notes: Rate constants for the self- and cross-termination of the isopropylol radical [(CH3)2ĊOH] and its anion [(CH3)2ĊO-] in aqueous solution are determined by kinetic electron spin resonance. Whereas the self-termination of the neutral radical occurs close to the diffusion-controlled limit, the cross- and self-terminations involving the anion are slower and reflect effects of charge repulsion and steric constraints by solvation.

Notes: The unimolecular decomposition of methyl nitrite in the temperature range 680-955 K and pressure range 0.64 to 2.0 atm has been studied in shock-tube experiments employing real-time absorption of CW CO laser radiation by the NO product. Computer kinetic modeling using a set of 23 reactions shows that NO product is relatively unreactive. Its initial rate of production can be used to yield directly the unimolecular rate constant, which in the fall-off region, can be represented by the second-order rate coefficient in the Arrhenius form: \documentclass{article}\pagestyle{empty}\begin{document}$$k_1 = 10^{17.90 \pm 0.21} \exp (- 17200 \pm 400/T){\rm cm}^{\rm 3} {\rm mol}^{ - 1} {\rm s}^{ - 1}$$\end{document} A RRKM model calculation, assuming a loose CH3ONO≠ complex with two degrees of free internal rotation, gives good agreement with the experimental rate constants.

Notes: Chemiluminescence from the a1Δ and b1Σ+ excited electronic states of nitrogen halide diatomics is observed when HN3 is allowed to react with mixtures of halogen atoms in a discharge-flow apparatus. Excited NF (a1Δ) is produced by the F + HN3 reaction, and NCl (a1Δ, b1Σ+) and NBr (a1Δ, b1Σ+) are produced by the F, Cl, + HN3 and F, Br + HN3 reactions, respectively. In the low-density limit, the yield of NF(a1Δ) was found to be near unity. The yields of the b1Σ+ states of NCl and NBr were determined to have a lower limit of ca. 10%. A number of results from these experiments, including direct observation of N3 radicals in the flow, support a hypothetical mechanism in which N3 acts as an intermediate. A second possible mechanism proceeding via an HNF intermediate cannot be ruled out.

Notes: Kinetics of the incorporation of mercury(II) ion in tetra (p-trimethylammoniumphenyl)porphine have been investigated in aqueous solution at 30.0°C and 0.2 M (NaNO3) ionic strength. The reaction was found to be first order each in mercury(II) and the porphyrin. The forward (formation) and the reverse (dissociation) rate constants were found to be 1.9 ± 0.2 × 103 M-1 s-1 and 7 ± 2 × 106 M-1 s-1, respectively. Kinetics of zinc(II) incorporation in tetra(p-trimethylammoniumphenyl)porphine catalyzed by mercury(II) were also investigated. This catalysis is explained in terms of steady-state formation of mono mercury(II) porphyrin followed by zinc(II) displacement of mercury(II) ion from the porphyrin. Such a mechanism also illustrates the importance of porphyrin core deformation to metal incorporation.

Notes: The yields of C5 and C6 alkyl nitrates from neopentane, 2-methylbutane, 2-methylpentane, 3-methylpentane, and cyclohexane have been measured in irradiated CH3ONONO-alkane-air mixtures at 298 ± 2 K and 735-torr total pressure. Additionally, OH radical rate constants for neopentyl nitrate, 3-nitro-2-methylbutane, 2-nitro-2-methylpentane, 2-nitro-3-methylpentane, and cyclohexyl nitrate, relative to that for n-butane, have been determined at 298 ± 2 K. Using a rate constant for the reaction of OH radicals with n-butane of 2.58 × 10-12 cm3 molecule-1 s-1, these OH radical rate constants are (in units of 10-12 cm3 molecule-1 s-1): neopentyl nitrate, 0.87 ± 0.21; cyclohexyl nitrate, 3.35 ± 0.36; 3-nitro-2-methylbutane, 1.75 ± 0.06; 2-nitro-2-methylpentane, 1.75 ± 0.22; and 2-nitro-3-methylpentane, 3.07 ± 0.08. After accounting for consumption of the alkyl nitrates by OH radical reaction and for the yields of the individual alkyl peroxy radicals formed in the reaction of OH radicals with the alkanes studied, the alkyl nitrate yields (which reflect the fraction of the individual RO2 radicals reacting with NO to form RONO2) determined were: neopentyl nitrate, 0.0513 ± 0.0053; cyclohexyl nitrate, 0.160 ± 0.015; 3-nitro-2-methylbutane, 0.109 ± 0.003; 2-nitro-2methylbutane, 0.0533 ± 0.0022; 2-nitro-2-methylpentane, 0.0350 ± 0.0096; 3- + 4-nitro-2-methylpentane, 0.165 ± 0.016; and 2-nitro-3-methylpentane, 0.140 ± 0.014. These results are discussed and compared with previous literature values for the alkyl nitrates formed from primary and secondary alkyl peroxy radicals generated from a series of n-alkanes.

Notes: The absolute rate constant for the OH + HCl reaction has been measured from 240 to 295 K utilizing the techniques of laser/flash photolysis-resonance fluorescence. The HCl concentrations were monitored continuously by ultraviloet and infrared spectrophotometry. The results can be fit to the following Arrhenius expression: \documentclass{article}\pagestyle{empty}\begin{document}$$k_1 = (4.6{\rm } \pm {\rm }0.3){\rm } \times {\rm }10^{ - 12} \exp [- (500{\rm } \pm {\rm }60)/T{\rm cm}^3 /{\rm molecule} \cdot {\rm s}$$\end{document} The rate constant values obtained in this study are 20-30% larger than those recommended previously for modeling of stratospheric chemistry.

Notes: The reaction \documentclass{article}\pagestyle{empty}\begin{document}${\rm Br} + {\rm CH}_3 {\rm CHO}\buildrel1\over\rightarrow{\rm HBr} + {\rm CH}_3 {\rm CO}$\end{document} has been studied by VLPR at 300 K. We find k1 = 2.1 × 1012 cm3/mol s in excellent agreement with independent measurements from photolysis studies. Combining this value with known thermodynamic data gives k-1 = 1 × 1010 cm3/mol s. Observations of mass 42 expected from ketene suggest a rapid secondary reaction: \documentclass{article}\pagestyle{empty}\begin{document}$${\rm Br} + {\rm CH}_3 {\rm CO}\buildrel2\over\rightarrow[{\rm CH}_3 {\rm COBr}]^* \buildrel3\over\rightarrow{\rm HBr} + {\rm CH}_2 {\rm CO}$$\end{document} in which step 2 is shown to be rate limiting under VLPR conditions and k2 is estimated at 1012.6 cm3/mol s from recent theoretical models for radical recombination. It is also shown that 0 ≤ E1 ≤ 1.4 kcal/mol using theoretical models for calculation of A1 and is probably closer to the lower limit. Reaction -1 is negligible under conditions used.

Notes: The photolysis of trans-3,4-dimethylcyclopentanone has been studied in the gas phase, principally at 313 nm. However, a few experiments have also been performed using laser sources at 308 and 325 nm. Additionally, experiments were also carried out using the cis isomer. The major products produced by all three wavelengths and in the temperature range 100 to 150°C were propene, 1,2-dimethylcyclobutane, carbon monoxide, and 3,4-dimethylpent-4-en-al. The formation of the cyclobutane was stereospecific and the effects of temperature, pressure, and wavelength on the relative product yields could be rationalized in terms of a mechanism involving the formation of a vibrationally excited triplet state which could yield both hydrocarbons and the aldehyde and a nonexcited triplet yielding only the aldehyde. Some high intensity experiments with an exciplex laser at 308 nm gave results which could be due to the occurrence of some two photon absorption by the cyclopentanone or absorption by an excited intermediate. The results are compared with those previously reported for other substituted cyclopentanones.

Notes: The use of the KMS method for the evaluation of the exponent by the experimentalist requires that a lag or retardation be chosen. The best choice of lag is discussed quantitatively. Its dependence upon the decade range of the data, the relative magnitude of the background, the level and character of the noise, the number and distribution of the data, and the weighted least-squares method of analysis are all detailed. A table of lags and error factors is given, for various ranges, backgrounds, and kinds of noise. Bias in the extracted rate (k), due to noise and treatment of the data, is also discussed.

Notes: The average downward collisional energy transfer (〈ΔEdown〉) is obtained for highly vibrationally excited tert-butyl chloride, both undeuterated and per-deuterated, with Kr, N2, CO2, and C2H4 bath gases, at ca. 760 K. Data are obtained using the technique of pressure-dependent very low-pressure pyrolysis. Reactant internal energies to which the data are sensitive are in the range 200-250 kJ mol-1. For C4H9Cl, the 〈ΔEdown〉 values (cm-1) are 255 (Kr), 265 (N2), 440 (CO2), and 585 (C2H4), and for C4D9Cl, 245 (N2), 370 (CO2), and 540 (C2H4). The uncertainties in these values are ca. 20% (40% for Kr); the uncertainties in the deuteration ratios are 10-15%. The value for Kr is in agreement with theoretical predictions of a biased random walk model for internal energy change in monatomic/substrate collisions. The effect of deuteration of 〈ΔEdown〉 is also in accord with that predicted by a modification of the theory. Extrapolated highpressure rate coefficients for the thermal decomposition of reactant are 1013.6 exp(-187 kJ mol-1/RT) s-1 (C4H9Cl) and 1014.2 exp(-196 kJ mol-1/RT) s-1 (C4D9Cl), in accord with other studies and the expected isotope effect.

Notes: The reaction mechanism of carbon dioxide with diethanolamine (DEA) is investigated using the stopped-flow method with optical detection in the ranges of concentration [DEA] = 0.111-8.4 × 10-2M and [CO2] = 2.94-5.6 × 10-3M. The comparison of the fast time-dependent light transmission change of a pH indicator with theoretical simulations of integrated rate equations requires a kinetic model in which a simple carbamate formation takes place simultaneously with hydration reactions, whose contributions are far from being negligible. A first-order reaction relative to DEA is thus found with a rate constant for carbamate formation smaller than usually predicted (110 ± 15M-1s-1 at 25°C). The equilibrium constant for the same reaction is also determined giving pKR = 5.3 at 25°C, in satisfactory agreement with values assumed so far.

Notes: The gas-phase equilibrium and rate constants for the isomerizations of 1,3,6-cyclooctatriene (136COT) to 1,3,5-cyclooctatriene (135COT) [reaction (1)] and bicyclo[4.2.0]octa-2,4-diene (BCO) to 135COT [reaction (-2)] have been measured between 390 and 490 K and between 330 and 475 K, respectively. The rate constant of reaction (1) obeys the Arrhenius equation \documentclass{article}\pagestyle{empty}\begin{document}$$k_{\rm 1} = 10^{10.93 \pm 0.08} {\rm exp}[- (115.9 \pm 0.7{\rm kJ}/{\rm mol})/RT]{\rm s}^{ - 1}$$\end{document} The corresponding equilibrium constant is given by the van′t Hoff equation \documentclass{article}\pagestyle{empty}\begin{document}$${\rm In K}_{\rm 1}^{\rm 0} = (0.24 \pm 0.04) + (13.78 \pm 0.15{\rm kJ}/{\rm mol})/RT$$\end{document} The strain energy of the 136COT ring is calculated to be 31.7 kJ/mol, based on the known value of 37.2 kJ/mol for 135COT, and ΔHf0(298 K) for gaseous 136COT is 196.3 kJ/mol. The rate constant of reaction (-2) obeys the Arrhenius equation \documentclass{article}\pagestyle{empty}\begin{document}$$k_{{\rm - 2}} = 10^{12.38 \pm 0.23} {\rm exp}[(- 106.9 \pm 1.5{\rm kJ}/{\rm mol})/RT]{\rm s}^{ - 1}$$\end{document} The equilibrium constant for 135COT ⇆ BCO fits the van′t Hoff equation \documentclass{article}\pagestyle{empty}\begin{document}$${\rm In K}_{\rm 2}^{\rm 0} = (- 1.20 \pm 0.02) - (0.40 \pm 0.07{\rm kJ}/{\rm mol})/RT$$\end{document} The strain energy of the BCO skeleton is calculated to be 108.3 kJ/mol, and ΔHf0(298 K) for gaseous BCO is 183.3 kJ/mol.

Notes: Absolute rate coefficients for the reactions of the hydroxyl radical with ethane (k1, 297-300 K) and propane (k2, 297-690 K) were measured using the flash photolysis-resonance fluorescence technique. The rate coefficient data were fit by the following temperature-dependent expressions, in units of cm3/molecule·s: k1(T) = 1.43 × 10-14T1.05 exp (-911/T) and k2(T) = 1.59 × 10-15T1.40 exp (-428/T). Semiquantitative separation of OH-propane reactivity into primary and secondary H-atom abstraction channels was obtained.

Notes: The reaction SO + SO →l S + SO2(2) was studied in the gas phase by using methyl thiirane as a titrant for sulfur atoms. By monitoring the C3H6 produced in the reaction \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm S} + {\rm CH}_3\hbox{---} \overline {{\rm CH\hbox{---}CH}_2\hbox{---} {\rm S}} \to {\rm S}_2 + {\rm C}_3 {\rm H}_6 (7) $\end{document}, we determined that k2 ≃ 3.5 × 10-15 cm3/s at 298 K.

Notes: 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.

Notes: The kinetics of the cerium(IV) oxidation of glycolic acid have been studied in the medium HClO4—Na2SO4—NaClO4 at varying organic substrate (HL), hydrogen, and bisulfate ion concentrations at 25.0°C and ionic strength 2.0M. Under the experimental conditions used (0.03 ≤ [H+] ≤ 0.5M; 0.02 ≤ [HSO4-] ≤ 0.1M; 0.01 ≤ [HL] ≤ 0.1M) the observed pseudo-first-order rate constant kobs has been found to follow the complex expression where the values of the various constants have been estimated by a nonlinear least-squares method. According to this expression the oxidation process occurs significantly through three simultaneous pathways. Moreover three equilibria involving cerium(IV) and HSO4- (or SO42-) ions are important from a kinetic point of view, whereas only two equilibria involving the corresponding complexes with the organic substrate are predominant.

Notes: The gas-phase elimination of ethyl 3-methylbutanoate and ethyl 3,3-dimethylbutanoate has been studied, in a static system, over the temperature range of 360-420°C and in the pressure range of 71-286 torr. The reactions are homogeneous, unimolecular, and follow a first-order rate law. The temperature dependence of the rate coefficients is given by the following Arrhenius equations: for ethyl 3-methylbutanoate, log k1 (s-1) = (12.70 ± 0.36) - (202.5 ± 4.4) kJ/mol/2.303RT, and for ethyl 3,3-dimethylbutanoate, log k1 (s-1) = (13.04 ± 0.08) - (207.1 ± 1.0) kJ/mol/2.303RT. Alkyl substituents at the acyl carbon of ethyl esters yield very close values in rates. Consequently it is rather difficult to offer some conclusion concerning the effect of these substituents.

Notes: The gas-phase reaction CH3SH + I2 has been studied spectrophotometrically over the temperature range of 476-604 K. It was found that the reaction undergoes H abstraction by I at ≤575 K, leading to the formation of MeSI and followed by a secondary reaction which leads to the formation of MeSSMe: Taking into consideration the effect of reaction (2), the equilibrium constant K1 (554 K) has been evaluated to be 0.025 ± 0.004. This value was combined with the estimated values S2980 (CH3SI, g) = 73.7 ± 1.0 eu and 〈ΔCp1,5540〉 = 0.87 ± 0.3 eu to obtain ΔH1,2980 = 4.03 ± 0.73 kcal/mol. This yields ΔHf2980 (CH3SI, g) = 7.16 ± 0.73 kcal/mol when combined with known thermochemical values for CH3SH, HI, and I2. A kinetic study was vitiated by the concurrent heterogeneous reaction of MeSH and I2 at lower temperatures and the rather complicated chemistry occurring at elevated temperatures. However, attempts at measuring rate constants at 554 K lead to a lower limit of ΔHf2980 (CH3S·, g) ≥ 29.5 ± 2 kcal/mol when an estimated value of A = 1010.8 ± 0.2 L/mol·s for the reactionc is used. DH2980 (CH3S-I) is estimated to be 49.3 ± 1.7 kcal/mol. The bond strengths of some divalent sulfurs and the reaction mechanisms are discussed. A crude estimate of DH0(H-CH2SH) = 96 ± 1 kcal has been obtained from the kinetic data.

Notes: The thermal unimolecular decomposition of diethyl carbonate-1,1,1,2,2-d5 has been examined in the high-pressure-limiting region. The observed chemistry is consistent with a simple, competitive two-channel model: The intramolecular isotope effect kH/kD has been determined, and the relative Arrhenius parameters for the two channels are given by \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{\rm H} /k_D = (0.80 \pm 0.18)\,\exp [(1140 \pm 260){\rm cal/mol/RT}] $$\end{document} over the temperature range of 540-620 K. These Arrhenius parameters predict an isotope effect kH/kD = 5.4 at 300 K.

Notes: The rate of formation of toluene from ethylbenzene was studied at atmospheric pressure in the temperature range of 600-725°C in conventional flow equipment. Residence times were 0.55-1.7 s, and initial partial pressures of ethylbenzene (H2O diluent) were 0.05-0.17 atm. The rate of appearance of toluene measures [1] the rate of the reaction C6H5C2H5 → C6H5CH3· + CH3·, with log k = 15.70 - 74.49 ± 3.2/θ. From the activation energy, E0 for the decomposition is estimated to be 72.2 ± 3.2 kcal/mol. The results are compatible with those of Esteban et al. [2], for which regression analysis gives log k1 = 14.79 - 70.76/θ. A composite, log k = 15.10 - 72.0/θ, fits both sets of data and is experimentally indistinguishable from Robaugh and Steina's [3] recent estimate by the VLPP technique or other estimates in the literature [4-6]. In light of the high overall conversion of ethylbenzene studied (2-80%), the industrial-type flow equipment, and the widely differing methods of characterization and analysis, the excellent agreement with the results of [2,3,5] is worthy of note. The data are compatible with current estimates of the heat of formation of benzyl radicals [6,7].

Notes: The kinetics of the pyrolysis of n-hexane was studied in a conventional static reactor over a temperature range of 650-840 K. The overall reaction is essentially first order with the kinetic parameters A = 1013.92 s-1 and EA = 260.3 kJ/mol. The distributions of the main products were analyzed by gas chromatography. A reaction model involving 240 elementary reactions was developed to describe the experimental rate data. The agreement of the model with experimental data was surprisingly good over a wide range of temperatures and pressures and up to medium extents of conversion. Methods for sensitivity studies based upon the quasi-stationary-state assumption (QSSA) were developed, and for a number of more detailed effects, such as self-inhibition, explanations could be given. It was also shown that the hexyl isomerization reactions influence strongly the product distribution. The outstanding capability of kinetic modeling with computer simulations in handling complex kinetic systems is demonstrated.

Notes: The pressure dependence of the first-order rate coefficient of oxetan and oxetan-2,2-d2 decomposition has been studied in the pressure range from about 7 kPa down to 0.01 kPa at various temperatures between 673 and 758 K. Experimental data were analyzed using RRKM theory. Interpretation of the fall-off curves lends support to the high-pressure Arrhenius parameters A = 1015.42s-1 and EA = 259.5 kJ/mol derived from measurements made in the pressure-independent range. Decomposition of oxetan is found to occur via biradical intermediates. Data for the kinetic isotope effect were used to derive kinetic parameters for the ring-opening elementary steps in oxetan and oxetan-d2 decomposition.

Notes: Kinetics of the Cu(II) ion-mediated acid decomposition of tris (dimethylglyoximato)nickelate(IV), Ni(dmg)32- (dmg2- = dimethylglyoximate dianion), are reported in aqueous medium in the range of 3.6 ≤ pH ≤ 6.6 at 35°C and μ = 0.57 M. The pseudo-first-order rate constants of the disappearance of Ni(IV) kobs(M) satisfy the equation \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{{\rm obs(M)}} = k_{ad} + k_{dec(M)} $$\end{document} where kad refers to the pseudo-first-order rate constants for the proton-assisted decomposition of the Ni(IV) complex determined independently and is a function of [H+], and kdec(M) to that for the Cu(II) ion-mediated route and is a function of [H+] and [Cu2+]. Both kobs(M) and kdec(M) are found to increase with increasing [Cu(II)]0, tending to attain limiting values at higher relative [Cu(II)]0. At low [Cu(II)]0 the kdec(M) is found to register a decrease with increasing pH in the pH range of 3.6-4.4, then an increase in the range of 4.4-5.76, and again a decrease in the range of 5.76-6.6. Results on the Cu(II) ion-mediated acid decomposition are interpreted in terms of a probable mechanism involving pH-dependent adduct formation equilibria involving the one-protonated and the two-protonated species of Ni(IV) and the various species of Cu(II) ion in the media, followed by rate-determining acid decomposition of the adduct(s) to give Ni(II) aq. and Cu(dmgH)2. While the two-protonated Ni(IV) complex apparently reacts about five orders of magnitude faster than the one-protonated species, the aquacopper(II) reacts about two orders of magnitude slower than the hydroxoaquacopper(II).

Notes: The kinetics of the gas-phase reaction of CH3F with I2 have been studied spectrophotometrically from 629 to 710 K, and were determined to be consistent with the following mechanism: A least-squares analysis of the kinetic data taken in the initial stages of reaction resulted in \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k_4 (M^{ - 1} \cdot s^{ - 1}) = (11.3 \pm 0.1) - (30.8 \pm 0.2)/\theta $$\end{document} where θ = 4.575T/1000 kcal/mol. The errors represent one standard deviation. The experimental activation energy E4 = 30.8 ± 0.2 kcal/mol was combined with the assumption E3 = 1 ± 1 kcal/mol and estimated heat capacities to obtain \documentclass{article}\pagestyle{empty}\begin{document}$$ \Delta H_r^\circ (4,g,298K) = 30.0 \pm 1{\rm kcal}/{\rm mol} $$\end{document} The enthalpy change at 298 K was combined with selected thermochemical data to derive \documentclass{article}\pagestyle{empty}\begin{document}$$ DH^\circ ({\rm CH}_{\rm 2} {\rm F} - {\rm H}) = 101.2 \pm 1{\rm kcal/mol} $$\end{document} The kinetic studies of ĊHF2 and CH2F2 have been reevaluated to yield \documentclass{article}\pagestyle{empty}\begin{document}$$ DH^ \circ \left( {{\rm CHF}_{\rm 2} - {\rm H}} \right) = 103.2 \pm 1\,{{{\rm kcal}} \mathord{\left/ {\vphantom {{{\rm kcal}} {{\rm mol}}}} \right. \kern-\nulldelimiterspace} {{\rm mol}}} $$\end{document} These results are combined with literature data to yield the C—H, C—F, and C—Cl bond dissociation energies in their respective fluoromethanes, and the effect of α-fluorine substitution is discussed.

Notes: Deliberate activation of the reaction vessel surface leads to the domination of chain termination in ethane pyrolysis by the reaction \documentclass{article}\pagestyle{empty}\begin{document}$$ (5) {\rm H} \to \frac{1}{2}{\rm H}_2 $$\end{document}As a result, chains are dramatically reduced in length, methane yields are entirely primary and larger in proportion to other products, and values of k1 \documentclass{article}\pagestyle{empty}\begin{document}$$ (1){\rm C}_2 {\rm H}_6 \to 2{\rm CH}_3 $$\end{document} can be directly determined from methane yield data without ambiguity. Experiments carried out in the temperature range of 841-913K at initial ethane pressures of 1-20 torr, without and with added nitrogen, yield the infinite pressure Arrhenius equation \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}k_{\rm 1} ({\rm s}^{ - 1}) = 16.52 \pm 0.44 - 87900 \pm 1760{\rm cal}/{\rm mol}/2.303RT $$\end{document}It is shown that most previously published data can be combined with those of this study to yield \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}k_{\rm 1} ({\rm s}^{ - 1}) = 16.63 \pm 0.18 - 88400 \pm 720{\rm cal}/{\rm mol}/2.303RT $$\end{document}Fall-off curves for k1 as a function of pressure are in good agreement with those from other laboratories. From these the relevant data for k-1 can be extracted for use in other kinetic studies.

Notes: The title reaction was studied in a standard flow system with F atoms produced by RF discharge in F2-He mixture. Analysis was by gas chromatography using electron capture detection. There were two major products, identified as CF2BrCF2H and CF2BrCF2Br, plus presumably HF which was not detectable. The overall rate of disappearance of reactant was found to be of mixed one and one-half order, indicating a complex reaction. A mechanism is proposed comprising six steps and involving two radical species CF2BrċFBr (R1) and CF2BrċF2. The 300 K rate constant for the initial step F + reactant → HF + R1 is evaluated to be 2.2 × 10-13 cm3/molec·s, which fits in with rates of other saturated hydrocarbon reactants containing one hydrogen atom, thus supporting the view that in this class of reactants the rates of reactions of the type F + saturated hydrocarbon depend mainly on the number of hydrogen atoms in the reactant.

Notes: The kinetics of the oxidation of dimethylsulfoxide by oxohydroxoosmate(VIII) complex ions in alkaline media follow pseudo-first-order disappearance in Os(VIII). The values of the observed pseudo-first-order rate constant are linearly dependent on initial dimethylsulfoxide concentrations in a fortyfold range, and increase with increasing [OH-], leveling off at higher relative [OH-]. The results are interpreted in terms of outer sphere interactions involving dimethylsulfoxide and various species of the Os(VIII) complex. The more nucleophilic dihydroxotetraoxoosmate(VIII) ion reacts about 50 times faster than the trihydroxotrioxoosmate(VIII) species.

Notes: The rate coefficient of the reaction \documentclass{article}\pagestyle{empty}\begin{document}$$(2){\rm H}_2 {\rm CN} \to {\rm H} + {\rm HCN}$$\end{document} has been determined in the temperature range of 2700-3500 K using a shock tube technique. C2N2—H2—Ar mixtures were heated behind incident shock waves and the early-time CN history was monitored using broad-band absorption spectroscopy. The rate coefficient providing the best fit to the data was \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm k = (7}{\rm .5}_{ - 2.0}^{{\rm + 2}{\rm .5}} {\rm)} \times {\rm 10}^{{\rm 13}} {\rm cm}^3 /{\rm mol} \cdot {\rm s} $$\end{document} in good agreement with extrapolations of previously published low-temperature results.

Notes: The photolysis of azocyclopentane in the presence of cyclopentane-carbon tetrachloride mixtures has been investigated in the gas phase. Product analysis data have been used to determine the Arrhenius parameters for the reactions \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {(4)_C - {\rm C}_5 {\rm H}_{9.} + {\rm CCl}_4 \to _C - {\rm C}_5 {\rm H}_9 + {\rm CCl}_{3.} } \hfill & {k_4 = 10^{9.0 \pm 0.6} {\rm exp}[- (10.3 \pm 1.0){\rm kcal}/{\rm mol}/{\rm RT}]} \hfill \\ {(6){\rm CCl}_{3.} + _C - {\rm C}_5 {\rm H}_{10} \to {\rm CCl}_3 {\rm H} + _C - {\rm C}_5 {\rm H}_{9.} } \hfill & {k_6 = 10^{8.4 \pm 0.4} {\rm exp}[- (10.0 \pm 0.7){\rm kcal}/{\rm mol}/{\rm RT}]} \hfill \\ \end{array}$$\end{document} The rate data for chlorine atom abstraction from CCl4 by the cyclopentyl radical were compared with available data for other alkyl radicals in both the gas and the solution phases. The results indicate that the rate constant for chlorine atom abstraction in the gas phase is fairly insensitive to the nature of the attacking alkyl radical and that the activation energy for a secondary radical is about 4 kcal/mol higher than the corresponding reaction in the solution phase.

Notes: Input data and results are presented for the calculation of a number of third-order rate constants of atmospheric interest using Troe′s approximate method. A comparison with experimental data indicates that this approach provides a reliable method for predicting unknown rate constants and estimating temperature dependences. These calculations form the basis of the recommendations of the NASA review panel for third-order rate constants to be used in atmospheric modeling.

Notes: We have reinvestigated temperature effects on the rates of hydrolysis of 0.0585M sucrose in 0.57M HCl solutions over the range of 10-40°C using polarimetry as a physical method to follow the reaction while simultaneously analyzing the solutions by HPLC for the disappearance of sucrose and by GLC for the appearance of glucose. When the polarimetric data are corrected for the mutarotation lag, the energy of activation values are the same by all three analytical methods and are temperature-independent.

Notes: The metathesis reaction of DI with t-C4H9 generated by 351-nm photolysis of 2,2′-azoisopropane was studied in a low-pressure reactor (VLPφ Knudsen cell) in the temperature range of 302-411 K. The data obeyed the following Arrhenius relation when combined with recent data by Rossi and Golden gathered by the same technique (t-C4H9 by thermal decomposition of 2,2′-azoisobutane): log k2D(M-1s-1) = 9.60 - 1.90/θ, where θ = 2.303RT kcal/mol for 302 K 〈 T 〉 722 K. The metathesis reaction of HI with t-C4H9 was studied at 301 K and resulted in k2H(M-1·s-1) = (3.20 ± 0.62) × 108. An analogous Arrhenius relation was calculated for the protiated system if the small primary isotope effect k2H/k2D was assumed to be √2 at 700 K. It was of the following form: log k2H(M-1·s-1) = 9.73 - 1.68/θ.Preliminary data of Bracey and Walsh indicate that earlier Arrhenius parameters determined for the reverse reaction are somewhat in error. Their value of log k1(M-1·s-1) = 11.5 - 23.8/θ yields 7delta;Hf,3000(t-butyl) = 9.2 kcal/mol and S3000(t-butyl) = 74.2 cal/mol7°K when taken in conjuction with this study.

Notes: The isomerization of 1-hexene on 70/80 mesh HY zeolite was studied at 200°C. The observed reaction products are formed via a variety of processes including double bond shift, cis-trans isomerization, skeletal rearrangement, cracking, hydrogen transfer, polymerization, cyclization, and coke formation. By applying the time-on-stream theory, the products have been classified as primary, secondary, or both, according to their OPE curves on product selectivity plots. 2-Ethyl-1-butene, which is present as an impurity in the feed, is found to react about 30 times faster than 1-hexene. Both 2-hexenes and 3 hexenes are formed primarily from 1-hexene, while 3 methyl 2 pentenes and 3-methyl-1-pentene formed from 2-ethyl-1-butene. The ratio of the initial rate of deprotonation to that of hydrogen shift in these reactions is ∼15 and ∼100, respectively. All products of skeletal rearrangement are observed to be secondary. Cracking products are produced mainly from precoke, which is also the source of hydrogen in the formation of paraffins. A detailed reaction network along with its associated mechanisms are presented and discussed.

Notes: The photochemical decomposition of peroxomonosulfate (PMS) in the presence and absence of 2-propanol at 25°C was found to obey an overall first-order rate - d[PMS]/dt = kφ[PMS]. In the absence of 2-propanol, the quantum yield ≤ for the decomposition of PMS was found to depend upon the concentration of PMS at [PMS] 〉 2 × 10-M, and is independent of concentration at [PMS] 〉 2 × 10-2M. The quantum yield in the presence of 2-propanol was found to be 3.03 at [PMS] = 1 × 10-2M and 4.45 at higher concentrations of PMS. In the pH range of 2-9.0 the quantum yield was found to be independent of pH, and the overall rate constant kφ was found to be 6.49 × 10-3 s-1 and 1.68 × 10-3 s-1, respectively, in the presence and absence of isopropanol. A suitable chain mechanism is proposed and explained.

Notes: Aqueous bromine reacts with alkyl-sidechain amino acids through a series of steps resulting in the formation of the corresponding alkyl aldelydes and nitriles. The kinetics and the mechanism of the interaction of bromine with alanine are examined. The products and the rates of this reaction are dependent in a complex way on the initial reactant concentration and pH. Acetaldeyde production is favored at low bromine-to-alanine ratios, low bromine concentrations, and pH values above 6. The first-order rate constant for the formation of acetaldelyde from alanine under these conditions is k4 = 1.98 × 1015 e-22,500/RT min-1. At higher concentration the nitrile is formed through a bromoimine intermediate. Under most conditions the nitrile appears to form from a catalyzed decomposition of the bromoimine which is too fast to be followed by the methods used in this study. However, residual amounts of the bromoimine decay by a slower first-order mechanism. The rate constant for this slower reaction in the case of alanine at pH 6.8-6.9 and alanine concentrations of 1 × 10-4M is k6 = 1.75 × 105 e-10,400/RT min-1.

Notes: Relative rate constants for the gas-phase reactions of OH radicals with a series of bi- and tricyclic alkanes have been determined at 299 ± 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 cyclohexane of 7.57 × 10-12 cm3/molec·s, the rate constants obtained are (× 1012 cm3/molec·s): bicyclo[2.2.1]heptane, 5.53 ± 0.15; bicyclo[2.2.2]octane, 14.8 ± 1.0; bicyclo[3.3.0]octane, 11.1 ± 0.6; cis-bicyclo[4.3.0]nonane, 17.3 ± 1.3; trans-bicyclo[4.3.0]nonane, 17.8 ± 1.3; cis-bicyclo[4.4.0]decane, 20.1 ± 1.4; trans-bicyclo[4.4.0]decane, 20.6 ± 1.2; tricyclo[5.2.1.02,6]decane, 11.4 ± 0.4; and tricyclo[3.3.1.13,7]decane, 23.2 ± 2.1. These data show that overall ring strain energies of ≲4-5 kcal mol-1 have no significant effect on the rate constants, but that larger ring strain results in the rate constants being decreased, relative to those expected for the strain-free molecules, by ratios which increase approximately exponentially with the overall ring strain.

Notes: Relative rate constants for the reaction of OH radicals with a series of α,β-unsaturated carbonyls have been determined at 299 ± 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 propene of 2.52 × 10-11 cm3/molec·s, the rate constants obtained are (× 1011 cm3/molec·s: acrolein, 1.83 ± 0.13; crotonaldehyde, 3.50 ± 0.40; methacrolein, 2.85 ± 0.23; and methylvinylketone, 1.88 ± 0.14). These data, which are necessary input to chemical computer models of the NOx-air photooxidations of conjugated dialkenes, are discussed and compared with literature values.

Notes: It is shown that, by deliberate activation of the reaction vessel, heterogeneous reaction at the wall can be made to dominate chain termination in a complex gas-phase reaction. For a homogeneous process, characterized, as is often the case, by multiple terminations, this has the effect of simplifying the mechanism and allowing explicit solution of the relevant steady-state equations so that the rate constants of some individual steps can be evaluated without assumption as to the values of those of others.The pyrolysis of propane, in the vicinity of 500°C, has been used as an example of this approach. Enhancement of the wall activity leads to the reaction providing, almost exclusively, chain termination. As a result, rate constants for the initiation step can be directly determined. The results of this study provide the Arrhenius equation \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k_1 (s^{ - 1}) = 16.71 \pm 0.54 - 83400 \pm 1950{\rm cal}/{\rm mol}/2.303RT $$\end{document} In combination with current thermochemical values this result gives k-1 = 1013.40 cm3/mol·s which, in turn, implies, via the geometric mean rule, kEt-Et = 1012.9 cm3/mol·s for ethyl-ethyl recombination, in good accord with the most recent determinations and compatible with the newly proposed value of the enthalpy of formation of ethyl.The first-order wall constant k8 has been evaluated as k8〈104.2 s-1. This appears to be the first occasion on which a wall constant has been evaluated from data for a high-temperature complex gas reaction.

Notes: The initial rates of formation of the major products in the thermal reactions of ethylene at temperatures in the neighborhood of 800 K have been measured in the presence and absence of the additives neopentane and ethane. It has been shown that in the absence of the additive the main initiation process is while in the presence of neopentane and ethane the following additional initiation processes occur: From the ratios of the rates of formation of the major products in the presence and absence of the additive the ratios kN/k1 and kE/k1 were measured over the temperature range of 750-820 K. Taking values from the literature for kN and kE, the following value was obtained for k1: \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k_1 ({\rm L}/{\rm mol} \cdot {\rm s}) = 11.27 \pm 0.6 - \frac{{64,200 \pm 2000}}{{2.3RT}} $$\end{document} Previous results using butene-1 as additive were rexamined and shown to be consistent with this measurement. From this measurement the following values were derived: ΔHf(C2H3) = 63.4 ± 2 kcal/mol and D(C2H3—H) = 103 kcal/mol.

Notes: An empirical approach to the kinetic investigations of photo-initiated liquid-phase chlorination of benzene is presented. Reaction order and the reaction constants for chlorine consumption and for the production of hexachlorocyclohexane isomers were evaluated from experimental data.

Notes: Thermochemical analysis of the electron capture process of SF6 leads to a rate constant for the reverse process \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm SF}_6^ - \mathop \to \limits^2 {\rm SF}_6 + e^ -,k_2 = 1.5 \times 10^{13 - 31.4/\theta } {\rm s}^{{\rm - 1}} $\end{document}, where θ = 2.303RT, in kcal/mol. The electron affinity of 32±3 kcal/mol is deduced from the observed bimolecularity of the capture process down to 0.1 torr Ar bath gas and estimated entropies of SF6 and SF6-. The capture process is discussed from the view point of the formation of a metastable SF6- electron (SF6·eL-) Langevin complex which appears to have a lifetime of about 2 × 10-13 s. Curve crossing from the SF6·eL- complex to vibrationally excited (SF6-)* appears to have a normal rate and A factor. This is interpreted to indicate near-resonant coupling between the orbiting electron and the vibronic motions of SF6, together with similarity in structure of SF6 and SF6-. It is shown that the apparent slowness of thermal electron ejection from SF6- is a result of an unfavorable equilibrium constant rather than a slow rate.

Notes: The kinetics of oxidation of methyl phenyl sulfoxide by chloramine-T (CAT) has been studied in buffered ethanol-water (1:1 v/v) of pH 7.0. The reaction was found to follow no simple-order kinetics. A possible mechanism is suggested involving three rate-controlling steps: (1) the reaction between RNHCl (R = CH3C6H4SO2) and the sulfoxide, (2) the disproportionation of RNHCl, and (3) the reaction between RNCl2 and the sulfoxide. A mixed-order rate law is derived as rate/[C][SO] = k1 + Kdk2[C]/[SA]. The rate law is found to be obeyed for the meta- and para-substituted phenyl methyl sulfoxides also. The ρ value is obtained using Hammett's σ constants. The ρ values obtained for the attack of both RNHCl and RNCl2 with the sulfoxides are almost the same, showing that both are converting the sulfoxide to the same intermediate. A chlorinium ion transfer is suggested.

Notes: The vacuum decomposition of sucrose and cellobiose has been observed in the 150-250°C temperature range. The predominant decomposition product of both sugars is H2O with less than 5% CO, CO2, CH2O, CH3CHO, CH3OH, and C2H5OH formed. The detailed rates and temperature dependences suggest that with the possible exception of C2H5OH, the minor products are formed in secondary reactions of the dehydration products. Further it is shown that the so-called “melting with decomposition” of a sugar is in reality a high-temperature dissolution of the disaccharide in the eliminated water.

Notes: The bond dissociation energies of tetramethyl germane, triethyl stibine, tetraethyl lead, and triethylphosphine were determined using the technique of very-low-pressure pyrolysis. Arguments are presented for log A ≥ 17.0. The respective dissociation energies ΔH298 are 83, 57, 54, and 68 (±2) kcal/mol. A consistent set of methyl bond energies to main group metals is determined from these and previous results, and is examined for trends. Bond energies for various radicals to tin are also derived.

Notes: Vibrationally excited OH in v = 9 [designated OH†(9)] was generated by the reaction of hydrogen atoms with ozone in a fast-flow discharge system at 300 ± 3 K and a total pressure of 1.1 ± 0.1 torr, with argon as the carrier gas. The addition of a species X, which can deactivate the OH†(9) or react with it, led to a decrease in the Meinel band chemiluminescent emission intensities at both 626 nm (9 → 3 band) and 519 nm (9 → 2 band), which were monitored as a function of the concentration of X. Application of the kinetic scheme developed previously for this chemical system gave the relative rate constant for the removal of OH†(9) by X. The relative rate constants determined in this study, taking O2 as the reference deactivator (kO2 = 1.0), are as follows: He ≤ 0.02; H2 ≤ 0.05; SF6 0.09 ± 0.01; CF4 0.19 ± 0.01; N2O 3.5 ± 0.4; NO 17.7 ± 1.5; H2O 74.3 ± 2.9; D2O 57.6 ± 2.0; NH3 61.3 ± 1.9; ND3 58.7 ± 1.6; SO2 7.1 ± 1.4; COS 8.4 ± 1.7; H2S 33.7 ± 8.4; CH4 1.56 ± 0.03; CD4 1.06 ± 0.06. Application of these relative rate constants to conditions in the upper atmosphere (60-100 km) suggests that OH†(9) is removed primarily by deactivation by O2, and at altitudes ≳90 km, possibly by O(3P). However, since O2 is unusually efficient for a homonuclear diatomic in deactivating OH†(9), it may not be the primary deactivator for the lower (v ≤ 8) vibrational levels. These results are compared to earlier studies of OH†(9), and possible mechanisms of interaction of OH†(9) with these molecules are discussed.

Notes: The reaction of C2F5 radicals with HCN has been studied over the range of 533-673 K using the pyrolysis of pentafluoroethyl iodide as the free-radical source. Arrhenius parameters for the reaction relative to C4F10 recombination are given by \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k_{\rm H} /k_{c^{1/2} } = (5.36 \pm 0.15) - (57.3 \pm 1.8)/\theta $$\end{document} where θ = 2.303RT kJ/mol and kH/kc1/2 is in cm3/2/mol1/2·s1/2.

Notes: The oxidation of naphthols by alkaline hexacyanoferrate(III), at constant ionic strength, gave coupled products. The rate of the reaction was dependent on the first powers of the concentrations of substrate, oxidant, and alkali. The activation energies were 31.8 and 34.5 kJ/mol for α naphthol and β naphthol, respectively. The reaction pathway was via the formation of a radical intermediate, which was detected by electron spin resonance spectroscopy.

Notes: The liquid-phase thermolysis of 1,2-dihydronaphthalene was studied in a batch reactor in the range of 350-400°C. The measured product distributions were in good agreement with calculations based on a free-radical scheme with rate constants estimated by thermochemical methods. The kinetic calculations were carried out by numerical integration and by the long-chain approximation (LCA), which yielded a closed-form solution.

Notes: Kinetic solvent isotope effects (KSIE) were measured for the hydrolyses of acetals of benzaldehydes in aqueous solutions covering the pH (pD) range of 1-6. For p-methoxybenzaldehyde diethyl acetal, kD+/kH+ = 1.8-3.1, depending on the procedure used to calculate the KSIE and on the pH (pD) range used as the basis for kH+(kD+). It is shown that this variation is an experimental artifact, and is a characteristic of KSIE measurements in general. It is recommended that kL+ be calculated from a least-squares fit of data to the equation kobs = kL+[L+], and that the KSIE be reported as kD+/kH+. The limitation remains, however, that the KSIE measured for a variety of substances over quite different pH (pD) ranges may not be comparable to more than ℜ20%. The source of these observations is discussed in terms of small changes in the activity coefficient ratios (a specific salt effect), including the solvent isotope effect on the activity coefficient ratio [eq. (3)].

Notes: The gas-phase elimination of several polar substituents at the α carbon of ethyl acetates has been studied in a static system over the temperature range of 310-410°C and the pressure range of 39-313 torr. These reactions are homogeneous in both clean and seasoned vessels, follow a first-order rate law, and are unimolecular. The temperature dependence of the rate coefficients is given by the following Arrhenius equations: 2-acetoxypropionitrile, log k1 (s-1) = (12.88 ± 0.29) - (203.3 ± 2.6) kJ/mol (2.303RT)-1; for 3-acetoxy-2-butanone, log ±1(s-1) = (13.40 ± 0.20) - (202.8 ± 2.4) kJ/mol (2.303RT)-1; for 1,1,1-trichloro-2-acetoxypropane, log ℜ1 (s-1) = (12.12 ± 0.50) - (193.7 ± 6.0) kJ/mol (2.303RT)-; for methyl 2-acetoxypropionate, log ℜ1 (s-1) = (13.45 ± 0.05) - (209.5 ± 0.5) kJ/mol (2.303RT)-1; for 1-chloro-2-acetoxypropane, log ℜ1 (s-1) = (12.95 ± 0.15) - (197.5 ± 1.8) kJ/mol (2.303RT)-1; for 1-fluoro-2-acetoxypropane, log ℜ1 (s-1) = (12.83 ± 0.15)- (197.8 ± 1.8) kJ/mol (2.303RT)-1; for 1-dimethylamino-2-acetoxypropane, log ℜ1 (s-1) = (12.66 ± 0.22) -(185.9 ± 2.5) kJ/mol (2.303RT)-1; for 1-phenyl-2-acetoxypropane, log ℜ1 (s-1) = (12.53 ± 0.20) - (180.1 ± 2.3) kJ/mol (2.303RT)-1; and for 1-phenyl-3-acetoxybutane, log ℜ1 (s-1) = (12.33 ± 0.25) - (179.8 ± 2.9) kJ/mol (2.303RT)-1. The Cα—O bond polarization appears to be the rate-determining process in the transmition state of these pyrolysis reactions. Linear correlations of electron-releasing and electron-withdrawing groups along strong σ bonds have been projected and discussed. The present work may provide a general view on the effect of alkyl and polar substituents at the Cα—O bond in the gas-phase elimination of secondary acetates.

Notes: The rates of electrophilic bromination of various donors follow complex kinetics which include both first-order and second-order dependences on bromine, especially in the less polar solvents. The second-order rate constant ks and the third-order rate constant kt are evaluated for alkene bromination in carbon tetrachloride, and they are compared to those already listed for the electrophilic brominations of substituted styrenes, arenes, and metal carbonyls in the extant literature. Despite the varying magnitudes of the second- and third-order rate constants for these diverse donors (and in different solvents), the ratio log(ks/kt) is remarkably invariant. The mechanistic implication of this unique observation is discussed in the context of charge transfer interactions which are common to the activated complexes in the electrophilic brominations of various donors.

Notes: Cyano-substituted methyl radicals (cyanomethyl-hand 2-cyano-2-propyl radicals) and syn-and anti-1-cyano-allyl radicals were generated, and their recombination kinetics in solution were investigated between -50 and +50°C by time-resolved electron-spin-resonance spectroscopy. The comparison of the activation energies for recombination with the activation energies of the solution viscosities proves that the dimerizations of the radicals are diffusion controlled with rate constants on the order of 108-109M-1·s-1. In the case of cyanomethyl radicals an additional pseudo-first-order process, hydrogen abstraction, was detected and analyzed kinetically. Product analyses support the kinetic measurements.

Notes: Hexafluoro-t-butoxy radicals have been generated by reacting fluorine with hexafluoro-2-methyl isopropanol: Over the temperature range of 406-600 K the hexafluoro-t-butoxy radical decomposes exclusively by loss of a CF3 radical [reaction (-2)] rather than by loss of a CH3 radical [reaction (-1)]: The limits of detectability of the product CF3COCF3, by gas-chromatographic analysis, place a lower limit on the ratio k-2/k-1 of ∼80. The implications of this finding in relation to the reverse radical addition reactions to the carbonyl group are briefly discussed.A thermochemical kinetic calculation reveals a discrepancy in the kinetics and thermodynamics of the decomposition and formation reactions of the related t-butoxy radical:

Notes: By pyrolyzing di-t-butyl peroxide over the temperature range of 405-450 K in the presence of hexafluoroacetone the kinetics of the addition reaction (1), CH3 + (CF3)2CO→; (CF3)2C(Ȯ)CH3, have been studied. Detailed analyses have shown that the principal product of the adduct radical, (CF3)2C(Ȯ)CH3, is CF3COCH3 from reaction (2), (CF3)2C(Ȯ)CH3 → CF3COCH3 + CF3. The rate constant of the addition reaction was determined to be k1(dm3/mol·s) = (1.1 ± 4.0) + 109 exp(-(3680 ± 480)/T) over the temperature range 405-450 K, based on the value k3 = 2.2 × 1010 dm3/mol·s for reaction (3), 2CH3 → C2H6. The results are discussed in relation to existing data for radical additions to carbonyl groups.

Notes: The kinetics of the oxidation of hydrogen iodide (HI + O2) at low temperature (414-499 K) in the gas phase by the method of iodination kinetics is complicated by a heterogeneous reaction between hydrogen iodide and oxygen. Present work leads to an upper limit for the bimolecular rate constant k1 for the first and rate-determining step These data are combined with an estimated A factor A1 = 109.3±0.2 L/mol·s (assuming a tight linear I···H···O -  transition state), to calculate the lower limit of the activation energy for the forward reaction E1. This leads to a minimum value for the heat of formation of the HO2 radical, ΔHf298°(HO2) 〈 3.0 kcal/mol.

Notes: The title reaction has been investigated in the temperature range of 403-446 K. Monoiodogermane and di-iodogermane together with hydrogen iodide were the main products, although at high conversions at least one other product was formed. GeH3I is clearly the primary product. Initial rates were found to obey the rate law \documentclass{article}\pagestyle{empty}\begin{document}$$ - \frac{{{\rm d[I}_{\rm 2} {\rm]}}}{{{\rm dt}}} = \frac{{k[{\rm I}_{\rm 2}]^{1/2} [{\rm GeH}_{\rm 4}]}}{{1 + k'[{\rm HI}]/[{\rm I}_2]}} $$\end{document} over a wide range of initial iodine and monogermane pressures. Secondary reactions (of GeH3I with I2) affect the subsequent kinetics, although at sufficiently high initial reactant ratios ([GeH4]0/[I2]0 ≥ 100) an integrated rate equation fits the data with the same rate constants as the initial rate expression.The observed kinetics are consistent with an iodine atom abstraction chain mechanism, and for the step \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm I}^{\rm .} + {\rm GeH}_4 \mathop {\hbox to 24pt{\rightarrowfill}} {\hskip-16pt ^{{\rm1}}}{\hskip1em} {\rm \dot GeH}_{\rm 3} + {\rm HI} $$\end{document} log k1 (dm3/mol·s) = (11.03 ± 0.13) - (52.3 ± 1.0 kJ/mol)/RT ln 10 has been deduced. From this the bond dissociation energy D(GeH3—H) = 346 ± 10 kJ/mol (82.5 kcal/mol) is obtained. The significance of this value, together with derived values for Ge-Ge and Ge-C bond strengths, is discussed.

Notes: A study has been made both of secondary reactions occurring during the reaction of I2 with GeH4, and of the direct reaction between I2 and GeH3I. Both these studies show that the abstraction reaction \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm I}^ \cdot + {\rm GeH}_{\rm 3} {\rm I} \to {\rm \dot GeH}_{\rm 2} {\rm I + HI} $$\end{document} occurs about 30 times faster than the reaction \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm I}^ \cdot + {\rm GeH}_{\rm 4} \to {\rm \dot GeH}_{\rm 3} {\rm + HI} $$\end{document} in the temperature range of 425-446 K. This information is used to show that iodine substitution weakens Ge-H bonds by 14.4 ± 2.5 kJ/mol and that D(H2IGe—H) = 332 ± 10 kJ/mol (79.3 kcal/mol). Possible reasons for the effects of halogen substituents on Ge—H and Si—H bond strengths are discussed.

Notes: The rate constants of gas-phase reactions of the hydroxyl radical with β-dimethylstyrene and acetone have been determined by a relative method at 298 K. The values obtained are β-dimethylstyrene (3.3 ± 0.5) × 10-11 cm3/molecule·s and acetone (6.6 ± 0.9) × 10-13 cm3/molecule·s. A simplified kinetic treatment of the experimental data shows that β-dimethylstyrene is stoichiometrically converted to benzaldehyde and acetone. In the photooxidation study of benzaldehyde, carbon dioxide was the only detected product. The ratio between carbon dioxide produced and benzaldehyde reacted was ≥1.

Notes: The reaction of OH radicals with CS2 has been investigated by the application of Fourier transform infrared spectroscopy using both photolytic and nonphotolytic competitive techniques in a 420-L reaction chamber at different pressures over the temperature range of 264-293 K. The measured effective rate constant was found to be dependent on total pressure, temperature, and the mole fraction of O2 present in the system. The products of the reaction were found to be COS and SO2 with one molecule of each being formed for every reacted CS2. A value of (2.7 ± 0.6) × 10-12 cm3/molecule·s was obtained as effective rate constant for the reaction at 293 K in 760 torr of synthetic air.

Notes: A new approach to the dynamic modeling of chemical kinetics is presented. The technique is based on systematic planning of computer experiments, which allows an empirical model for the computed responses to be developed in the space of parameters. The empirical equations which are obtained provide complete information on the sensitivities with respect to various rate constants, disclosing their interrelationships. Utilization of these equations instead of numerical integration of the differential equations associated with the chemical reactions makes parameter estimation a trivial task. As a consequence the adequacy of the mechanism can be tested. The technique is applied to the thermal decomposition of propane.

Notes: The system of a sequence of five first-order reactions, A → B → C → D → E → F, has been analyzed kinetically. An actual example is proposed in the reaction of mesitonitrile in 89.8% (w/w) sulfuric acid at 98.3°C. The analysis provides estimates of concentration ratios as functions of time, and the progress of the buildup and decay of the intermediate species can be monitored. The kinetics have been measured for the hydration of mesitonitrile, the hydrolysis of mesitamide, and the sulfonation of mesitylenesulfonic acid in 89.8% sulfuric acid. The calculated values of the concentration ratios of mesitylenedisulfonic acid as a function of time were satisfactorily close to those found in experiment.

Notes: Theoretical rate constants have been calculated for O(3P) with five saturated hydrocarbons, CH4, C2H6, C3H8, iso-C4H10, and neo-C5H12. The method of choice is bond energy-bond order (BEBO) with activated complex theory (ACT). Because the BEBO method is empirical, O(3P) + CH4 is evaluated first, and the theoretical results are compared to more rigorous calculations and to the empirical transition state method. Comparisons are also made between predictions and experimental results. All of these comparisons show that the BEBO-ACT method gives results which are consistent with experiment and other theory. Because the method is successful, the other four cases are then considered. Ambiguity arises for the higher hydrocarbons from the problem of internal rotations in the activated complexes, and three cases are evaluated. Best agreement with experiment is obtained if the primary rotor(s) in the complexes are considered to be free. Predictions of rate constants are made from 500 to 2500 K. Throughout the discussion issues of theory which are common to any ACT calculation from any method of potential energy evaluation (LEP, LEPS, or ab initio quantum mechanics) are featured.

Notes: Rate constants for the gas-phase reactions of O3 with a series of cycloalkenes and with cis-2-butene have been determined at 297 ± 1 K. The rate constants obtained were (in units of 10-16 cm3/molecule·s): cis-2-butene, 1.38 ± 0.16; cyclopentene, 2.75 ± 0.33; cyclohexene, 1.04 ± 0.14; cycloheptene, 3.19 ± 0.36; 1,3-cyclohexadiene, 19.7 ± 2.8; 1,4-cyclohexadiene, 0.639 ± 0.074; bicyclo[2.2.1]-2-heptene, 21.4 ± 3.5; bicyclo[2.2.1]-2,5-heptadiene, 46.8 ± 12.9; and bicyclo[2.2.2]-2-octene, 0.728 ± 0.090. These data for cis-2-butene, cyclopentene, and cyclohexene are compared with previous literature data, and the effects of ring strain on the rate constants are discussed.