The reaction was investigated in the gas phase over the range 80–225°C using the photolysis of heptafluoroisopropyl iodide as the source of radicals. The rate constant, based on the value of 1013.36 cm3 mol?1 s?1 for the recombination of i-C3F7 radicals, is given by where θ = 2.303 RT/cal mol?1. Arrhenius parameters for chlorine abstraction from CCl4 by CF3, C2F5, n-C3F7, and some hydrogenated radicals are compared. 相似文献
Reaction of nucleogenic dimethylgermylium cations with benzene in the gas phase was studied by the radiochemical method. The
formation of the products of germylation of benzene, dimethylphenylgermane, and phenylgermane is indicative of the formation
of dimethylgermylium cations by the β-decay of tritium in the molecule of dimethylditritium germane. Dimethylgermylium cations
are shown to undergo a rearrangement in the course of the reaction with benzene, which is consistent with the earlier results
of quantum-chemical calculations. 相似文献
Gas phase reaction of dichlorogermylenes formed in the systems GeCl4-Si2Cl6 or Ge-GeCl4 with 1,2-dichloroethylene and trichloroethylene was studied. It is shown that:GeCl2 inserts into the C-Cl bond of 1,2-dichloroethylene and forms the derivatives with one or two trichlorogermyl groups. A specific feature of the reaction of:GeCl2 with trichloroethylene was found. In this reaction the formation of only monosubstituted compounds like 1,1-dichloro-2-trichlorogermylethylene and 1,2-dichloro-1-trichlorogermylethylene takes place. The rule established is valid in general also for the reaction of trichloroethylene with dichlorosilylene, another analog of carbene. Reactions taking place in the course of synthesis of organochlorogermanes are considered. 相似文献
The mechanism of unimolecular 1,1-elimination of H2 from carbocations has been investigated by the semiempirical MNDO method in view of its very good performances in the analogous elimination from H2CO. Contrary to previous suggestions, the critical configuration obtained at the MNDO level is characterized by a reduced symmetry with respect to the reacting molecule and by a very short H? H distance. RRKM computations of the rate constants and isotope effect employing MNDO results for the activation energies and vibrational frequencies indicate also that the present, nonsynchronous mechanism is compatible with all the available experimental data. 相似文献
The reactions between nitrogen dioxide and trimethyl- and triethylsilane have been studied. Under certain conditions ignition can occur. The main features of the reacting system are discussed and a reaction mechanism is proposed. 相似文献
The kinetics of the gas phase reactions of NO2 with a series of organics have been studied at 295 ± 2 K. It was observed that only 2,3-dimethyl-2-butene and the conjugated dialkenes studied reacted at observable rates, with rate constants which ranged from 1.5 × 10?20 cm3 molecule?1 s?1 for 2,3-dimethyl-2-butene to 1.3 × 10?17 cm3 molecule?1 s?1 for α-phellandrene. These rate constants are compared with the available literature data and the mechanisms of these reactions are discussed. 相似文献
Photolysis of the vapour of hexafluoroacetylacetone HFAA in its enolic form involves decomposition by two independent primary processes, one of which is a novel elimination of HF giving 2,2-difluoro-2,3-dihydro-5-trifluoromethylfuran-3-one: The HF is not vibrationally excited. Photolysis of the cyclic product of reaction (5) yields CF2 radicals which, if HFAA is present, undergo an insertion into the enolic OH bond, (9) The infrared, ultraviolet, nuclear magnetic resonance, and mass spectra of HFAA and of the products of reactions (5) and (6) have been measured. Approximate quantum yields for reactions (1) and (5) have been obtained. Both ?1 and ?5 depend on pressure and the ratio ?1/?5 increases with temperature and decreased wavelength of photolysing light. It is proposed that the ratio ?1/?5 increases as the vibrational energy of electronically excited HFAA increases. 相似文献
Chromones were measured by using electrospray ionization mass spectrometry in negative mode. Interestingly, in addition to the deprotonated ion ([M ? H]?), unexpected [M + 17]? and [M + 31]? ions were observed in high intensity when water and methanol were used as the solvent. Chromones with different substitutes were tested. Compared with the deprotonated ion, [M + 17]? and [M + 31]? ions were observed with higher abundances when the C‐3 site of chromones was substituted by electron withdrawing groups. Based on high performance liquid chromatography‐mass spectrometry (LC‐MS), deuterium‐labeling and collisional‐induced dissociation experiments, a covalent gas‐phase nucleophilic addition reaction between chromone and water, and the formation of a noncovalent complex between chromone and methanol were proposed as the mechanism for the observed [M + 17]? and [M + 31]? ions, respectively. Understanding and using these unique gas phase reactions can avoid misannotation when analyzing chromones and their metabolites. 相似文献
<正>The mechanisms for CH_3- and CH_4-elimination in the gas phase reaction of ground-state Zr with 2-butyne has been investigated in detail using B3LYP method.For the elimination of CH_3,two mechanisms which are similar to those previously found for the reactions of Y and Zr with propyne are identified.The mechanism for the elimination of CH_4 was revealed as:Zr + CH_3C≡CCH_3→π-complex→TS(H-migration)→HZr-(H_2CCC)-CH_3→TS(C-C insertion)→(H_2CCC)-HZr-CH_3→TS(H-migration)→CH_4+ ZrC_3H_2. 相似文献
Møller-Plesset MP2/6-31G method was used to examine the gas-phase elimination of 2-substituted alkyl ethyl N,N-dimethylcarbamates. The results of these calculations support a concerted non-synchronous six-membered cyclic transition state mechanism for carbamates containing a Cβ–H bond at the alkyl side of the ester. These substrates produce the N,N-dimethylcarbamic acid and the corresponding olefin. The unstable intermediate, N,N-dimethylcarbamic acid, rapidly decomposes through a four-membered cyclic transition state to dimethylamine and CO2 gas. Correlation of the logarithm of theoretical rate coefficients against original Taft's σ* values gave an approximate straight line (ρ*=−1.39, r=0.9558 at 360 °C). In addition to this fact, when log krel is plotted against the theoretical log krel for 2-substituted ethyl N,N-dimethylcarbamates a reasonable straight line (r=0.9919 at 360 °C) is obtained, suggesting similar mechanism. 相似文献
The relative rate technique has been used to determine the rate constants for the reaction of chlorine atoms with a series of oxygenated organic species. Experiments were performed at 295 ± 2 K and atmospheric pressure of synthetic air or nitrogen. The decay rates of the organic species were measured relative to that of ethane or n-butane. Using rate constants of 5.7 × 10?11 cm3 molecule?1 s?1, and 2.25 × 10?10 cm3 molecule?1 s?1 for the reaction of Cl with ethane and n-butane respectively the following rate constants were derived, in units of 10?11 cm3 molecule?1 s?1: propane, (16.0 ± 0.4);i-butane, (15.1 ± 0.9) n-pentane, (31.0 ± 1.6); n-hexane, (34.5 ± 2.3); cyclohexane, (36.1 ± 1.5); methanol, (4.57 ± 0.40); ethanol, (8.45 ± 0.91); n-propanol, (14.4 ± 1.2); t-butylalcohol, (3.26 ± 0.19); acetaldehyde, (8.45 ± 0.79); propionaldehyde, (11.3 ± 0.9); dimethylether, (20.5 ± 0.8); diethylether, (35.6 ± 2.8); and methyl-t-butylether, (16.6 ± 1.2). Quoted errors represent 2σ, and do not include any errors due to uncertainties in the rate constants used to place our relative measurements on an absolute basis. The results are discussed with respect to the mechanisms of these reactions and to previous literature data. 相似文献
The pyrolysis of phenylazoethane has been studied in a stirred-flow system using cyclohexene as carrier gas at sub-ambient pressures, in the temperature range of 380–416°C. The activation energy is examined in relation to the C–N bond dissociation energy and the heat of formation of the phenyldiazenyl radical.
Pure gaseous cyclopentene is found to polymerize on a glass surface when the polymerization is initiated with tungsten hexachloride. The polymer thus formed is colourless and has a high molar mass with a narrow molecular mass distribution. Polymerizations are carried out in the 10 to 60° C temperature range. From kinetic measurements, an overall activation energy of 69,0 kJ is obtained for the conversion of gaseous monomer to condensed polymer. NMR analyses show a distribution of cis-and trans-configurations of the double bonds in the polymer and the absence of any detectable branching. 相似文献
The slow gas-phase oxidation of tetrahydrofuran was studied under static conditions at 220°C. The relative amounts of each product, if extrapolated to zero reaction time, show which are the primary reaction products, and the reaction stoichiometry was thus established. Rate constants for hydroperoxides production and consumption were calculated; these hydroperoxides are responsible for chain branching. Carbon monoxide and carbon dioxide have been shown to be formed in the early stages of the reaction and not simply as end products of oxidative degradation processes. It has been found that at reaction times close to zero one tetrahydrofuran molecule may be attacked in one or several carbon atoms. 65.9% of tetrahydrofuran consumed in the first stages of the reaction forms succinic acid through a mechanism in which one molecule of fuel is attacked by two molecules of oxygen. More than 20% of the tetrahydrofuran molecules are attacked at least by three molecules of oxygen. 相似文献
The gas phase elimination of methyl 3-bromopropionate has been studied in a static system and in vessels seasoned with allyl bromide. The reaction is autocatalyzed by HBr. However, under maximum inhibition with propene, the reaction obeys first order kinetics and is a homogeneous unimolecular elimination. The products are methyl acrylate and hydrogen bromide. The observed rate coefficients are represented by the Arrhenius equation: log k1 (s–1)=(12.94±0.46)–(214.5±6.0) kJ/mol/2.303 RT in the temperature range 400.1–449.9 °C and pressure range 49–98 Torr. The pyrolysis of methyl 3-bromopropionate is 3.5 times faster than that of ethyl bromide. This significant difference may be attributed to the greater acidity of the -hydrogen in 3-bromopropionate compared to that in ethyl bromide.
The pyrolysis of diisopropyl disulfide was studied in a static system over the temperature range 274–304 °C at subambient pressures. The mechanism was examined by the pyrolysis of 3,4-dithia-2,5-dideuterohexane. The inhibited rate of consumption yielded the Arrhenius parameters logA=14.37±0.36; Ea=(192±4) kJ/mol.