Reaction of methyl radicals with haloalkanes

The kinetics of reactions involving halogen atom abstraction from haloalkanes by methyl radicals have been studied in the gas phase. Arrhenius parameters for halogen atom transfer were determined relative to those for methyl radical combination:

Competitive study of the reactions Br + RFI → IBr + RF and determination of bond dissociation energies D(RF−I) where RF = CF3, C2F5, n-;C3F7, i-C3F7, and n-C4F9

The overall photobromination reactions have been studied using a competitive technique. Relative Arrhenius parameters were obtained for the rate-determining step These were placed on an absolute basis using previous-absolute values of A and E for R_FI=CF₃I. The activation energies were used to calculate bond dissociation energies D(R? I) with the following results:

Measurement of absolute rate data for the reaction of ground state atomic silicon,Si(33PJ), with halogenated olefinic and aromatic compounds by time-resolved atomic resonance absorption spectroscopy

We present a kinetic study of the reaction of ground state silicon atoms with halogenated unsaturated organic compounds (R). Si(3³P_J) was generated by the repetitive pulsed irradiation of SiCl₄ in the presence of excess helium buffer gas and the reactant R in a slow flow system, kinetically equivalent to a static system. The ground state atom was monitored by time-resolved atomic resonance absorption spectroscopy at λ = 252 nm [Si(4³P_J) ← Si(3³P_J)] on time scales by which the optically metastable tates,Si(3¹D₂) and Si(3¹S₀) had relaxed to the ³P state, using signal averaging methods. Computerized fitting of the resulting atomic decay traces in the presence of the various reactants, R, yielded the following new body of absolute second-order rate constants (k_R, T = 300 K, errors = 2sigma;):

Gas phase reactions of CF3, C2F5, and n-C3F7 with carbon tetrachloride

The reactions of some perfluoroalkyl radicals with carbon tetrachloride have been studied using the photolysis of the corresponding perfluoroalkyl iodide as the free radical source. The Arrhenius parameters, based on the value of 2.3 × 10¹³ cm³ mol^?1 s^?1 for the self-combination rate constant of all radicals are:

Measurement of absolute rate data for the reaction of atomic potassium,K(42S½), with CH3F,C2H5F,C6H5F,CH3Br,C2H5Br,HCl and HBr by time-resolved atomic resonance absorption spectroscopy at λ = 404 nm (K(52PJ) ← K(42S½))

We present a kinetic study of atomic potassium in its electronic ground state, K(4²S_½), generated in the “single-shot mode” by pulsed irradiation at elevated temperatures and monitored by time-resolved atomic resonance absorption spectroscopy using the Rydberg doublet at λ = 404 nm (K[5²P_J]←K[4²S_½]). Profiles for the decay of atomic potassium in the presence of various halogenated reactants were recorded at different temperatures, yielding the following Arrhenius parameters (k_R = A exp(?E/RT), errors 1σ):

Relative rate constants for the reactions of hydroxyl radicals and chlorine atoms with a series of aliphatic alcohols

Rate constants for the gas‐phase reactions of hydroxyl radicals and chlorine atoms with a series of alcohols have been determined by using the relative method. The experiments were performed at 295 ± 2 K and at 1 atmospheric pressure. The obtained values of the rate constants in units of 10^?12 cm³ molecule^?1 s^?1 are as follows:

The reactions of CF3 radicals with cyclanes and the determination of C?H bond dissociation energies in cyclanes

The reactions of CF₃ radicals with the C₃ to C₇ cyclanes and spiropentane were studied and the following Arrhenius parameters were obtained for the reaction CF₃ + c-RH → CF₃H + c-R:

Kinetic investigation of the collisional behavior of ground state atomic carbon,C(2p2(3PJ)), with halogenated olefins and aromatic compounds studied by time-resolved atomic resonance absorption spectroscopy in the vacuum ultra-violet

A kinetic investigation is described of the reaction of ground state atomic carbon, C(2p²(³P_J)), monitored by time-resolved atomic resonance absorption spectroscopy, with a wide range of halogenated olefins and aromatic compounds. Atomic carbon was generated by the repetitive pulsed irradiation (λ > ca. 160 nm) of C₃O₂ in the presence of excess helium buffer gas and the added reactant gases in a slow flow system, kinetically equivalent to a static system. C(2³P_J) was then monitored photoelectrically by time-resolved atomic resonance absorption in the vacuum ultra-violet (λ = 166 nm, 3³P_J ← 2³P_J) with direct computer interfacing for data capture and analysis. The following absolute second-order rate constants for the reactions of C(2³P_J) with the following reactants are reported:

Abstraction of chlorine atoms from polychloroethanes. IV. The kinetics of chlorine abstraction from 1,1,2-trichloroethane, 1,1-dichloroethane,and 1,2-dichloroethane by cyclohexyl radicals

The kinetics of chlorine atom abstraction from the chloroethanes (EClH) 1,1,2-C₂Cl₃H₃, 1,1-C₂Cl₂H₄, and 1,2-C₂Cl₂H₄ by radiolytically generated cyclohexyl radicals was studied in the liquid phase by a competitive method. The chlorine atom abstraction data were put on an absolute basis by comparing the rates of the metathetical reactions with the known rate of addition of cyclohexyl radicals to C₂Cl₄. The following Arrhenius parameters were obtained:

A relative rate study of the reaction of chlorine atoms (Cl) and hydroxyl radicals (OH) with a series of ethers

Rate constants for the gas phase reactions of hydroxyl radicals and chlorine atoms with a number of ethers have been determined at 300 ± 3 K and at a total pressure of 1 atmosphere. Both OH radical and chlorine atom rate constants were determined using a relative rate technique. Values for the rate constants obtained are as follows.

Arrhenius parameters for reactions of oxygen atoms with the fluorinated ethylenes

Competitive studies of the reactions of ground-state oxygen atoms, generated by mercury-photosensitized decomposition of nitrous oxide, have been carried out with ethylene and all the fluoroethylenes using 2-(trifluoromethyl)-propene as reference compound. From measurements at 25°C and 150°C relative rate constants have been determined and used to calculate the Arrhenius parameters shown in the following table:

Rate constants for the gas-phase reactions of OH radicals and Cl atoms with n-alkyl nitrites at atmospheric pressure and 298 K

Rate constants for the reactions of OH radicals and Cl atoms with CH₃ONO, C₂H₅ONO, n-C₃H₇ONO, n-C₄H₉ONO, and n-C₅H₁₁ONO have been determined at 298 ± 2 K and a total pressure of approximately 1 atm. The OH rate data were obtained using both the absolute rate technique of pulse radiolysis combined with kinetic spectroscopy and a relative rate method involving simultaneous measurement of the loss of the nitrite and the reference compound. The Cl rate constants were measured using the relative rate method. Values of the rate constants in units of 10^?13 cm³ molecule^?1 s^?1 are:

Hydrogen-abstraction reactions from organosilicon compounds. The reactions of methyl,trideuteromethyl, trifluoromethyl,and ethyl radicals with tetramethylsilane

The following Arrhenius parameters have been determined for the hydrogen-abstraction reactions: R + (CH₃)₄Si → RH + (CH₃)₃SiCH₃

Hydrogen abstraction from organosilicon compounds. The reactions of fluoromethyl radicals with tetramethylsilane. Polar effects in gas phase reactions

The photolysis of 1,1,3,3-tetrafluoroacetone has been reinvestigated as a source of CHF₂ radicals at temperatures up to 578°K, and the following rate constant ratio was determined for the reactions

1 θ= 2.303 RT in kcal/mole.

1,1-Difluoro- and 1,1,3,3-tetrafluoroacetone were photolyzed in the presence of tetramethylsilane, and Arrhenius parameters were measured for the hydrogen abstraction reactions: R + Me₄Si → RH + Me₃SiCH₂

Comprehensive inter‐laboratory calibration of reference materials for δ18O versus VSMOW using various on‐line high‐temperature conversion techniques

Internationally distributed organic and inorganic oxygen isotopic reference materials have been calibrated by six laboratories carrying out more than 5300 measurements using a variety of high‐temperature conversion techniques (HTC) a in an evaluation sponsored by the International Union of Pure and Applied Chemistry (IUPAC). To aid in the calibration of these reference materials, which span more than 125‰, an artificially enriched reference water (δ¹⁸O of +78.91‰) and two barium sulfates (one depleted and one enriched in ¹⁸O) were prepared and calibrated relative to VSMOW2 b and SLAP reference waters. These materials were used to calibrate the other isotopic reference materials in this study, which yielded:

Hydrogen abstraction reactions from organosilicon compounds. The reactions of fluoromethyl radicals with trichlorosilane. The photolyses of di- and tetrafluoroacetone

The photolyses of 1,3-difluoro- and 1,1,3,3-tetrafluoroacetone have been reinvestigated as sources of fluoromethyl radicals, and the following rate constant ratios were determined

1 θ= 2.303 RT in kcal/mole.

The results are in substantial agreement with the original investigations. The photolyses of the fluoroacetones were used as sources of CH₂F and CHF₂ radicals, and the following Arrhenius parameters were obtained for the hydrogen abstraction reactions R + SiHCl₃ → RH + SiCl₃:

Abstraction of chlorine atoms from chloromethanes by the cyclohexyl radical

The kinetics of chlorine atom abstraction from the chloromethanes (CM)CCl₄, CHCl₃, and CH₂Cl₂ by radiolytically generated cyclohexyl radicals has been studied in the liquid phase by a competitive method. The halogen abstraction data have been put on an absolute basis by comparing the rates of the metathetical reactions with the known rate of addition of cyclohexyl radicals to C₂Cl₄. The following Arrhenius parameters were obtained:

Hydrogen abstraction reactions from organosilicon compounds. The reactions of methyl,trifluoromethyl, and ethyl radicals with trichlorosilane

Arrhenius parameters have been determined for the hydrogen-abstraction reactions: R + SiHCl₃ + RH + SiCl₃

Kinetics of gas-phase addition reactions of methyl radicals. I. Addition to ethylene,acetylene, and benzene

The reactions have been studied by a mass-balance method involving the photolysis of small amounts of biacetyl in the presence of a large excess of isobutane containing a small proportion of the unsaturated substrate. The following Arrhenius parameters have been derived:

Kinetics of the reactions of OH radicals with selected acetates and other esters under simulated atmospheric conditions

The relative hydroxyl radical reaction rate constants from the simulated atmospheric oxidation of selected acetates and other esters have been measured. Reactions were carried out at 297 ± 2 K in 100-liter FEP Teflon®-film bags. The OH radicals were generated from the photolysis of methyl nitrite in pure air. Using a rate constant of 2.63 × 10^?11 cm³ molecule^?1 s^?1 for the reaction of OH radicals with propene, the principal reference organic compound, the rate constants (×10¹² cm³ molecule^?1 s^?1) obtained for the acetates and esters used in this study are: