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1.
Ultraviolet absorption spectra have been characterized for the acetyl-h3 and acetyl-d3 radicals, which were generated by the flash photolysis of the corresponding acetones. The spectra are broad and intense, with values of the extinction coefficient at the respective maxima estimated as: ?CH3CO(215) = (1.0 ± 0.1) × 104 L/mol·cm and ?CD3CO(207.5) = (1.0 ± 0.05) × 104 L/mol·cm. Rate constants for the reactions of mutual interaction were estimated as: k = 3.5 × 1010 L/mol·s and k = 3.4 × 1010 L/mol·s. Rate constants for the reactions of cross interaction were estimated as: k = 8.6 × 1010 L/mol·s and k = 5.2 × 1010 L/mol·s. The related values of the cross interaction ratios k/(kk)1/2 = 2.6 and k/(kk)1/2 = 1.6 do not differ significantly from the statistical value of 2. The participation of the radical displacement reactions was estimated in terms of the fractions k/k = 0.38 and k/k = 0.47. Corroborative spectra were obtained from the flash photolysis of methyl ethyl ketone and biacetyl, and the relative rates of the competing primary processes were estimated from the relative peak heights of the acetyl and methyl radicals in each system. 相似文献
2.
The hexacyanoferrate(III)-thallium(I) reaction in aqueous acetic acid containing large concentrations of hydrochloric acid is considerably accelerated both by hydrogen and chloride ions as well as increasing acetic acid in the medium. The experimental results obey the rate law (1) where β1 to β6 are the cumulative stability constants of the species TlCl, TlCl, TlCl, HFe(CN), H2Fe(CN) and H3Fe(CN)6 respectively and ka and kb are the rate constants associated with the mono- and di-protonated oxidant species. The main active species are H2Fe(CN) and TlCl. 相似文献
3.
The kinetics of the permanganate oxidation of formic acid in aqueous perchloric acid has been studied. The results indicate that this reaction is autocatalyzed by both manganese(II) ion (formed as a reaction product) and colloidal manganese dioxide (formed as an intermediate). The apparent rate constants corresponding to the noncatalytic and autocatalytic reaction pathways are given, respectively, by the following equations The activation energies associated with the true rate constants, ??, ??, ??, ??, ??, and ?? are 37.2, 62.5, 70.9, 52.5, 40.8, and 59.9 kJ mol?1, respectively. The percentage of the total reaction corresponding to each pathway is given for typical experimental conditions. Mechanisms in agreement with the kinetic data are proposed for the six different reaction pathways observed. 相似文献
4.
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 SF. The capture process is discussed from the view point of the formation of a metastable SF electron (SF6·e) Langevin complex which appears to have a lifetime of about 2 × 10?13 s. Curve crossing from the SF6·e complex to vibrationally excited (SF)* 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 SF. It is shown that the apparent slowness of thermal electron ejection from SF is a result of an unfavorable equilibrium constant rather than a slow rate. 相似文献
5.
Yueh-Tai Fanchiang 《国际化学动力学杂志》1984,16(3):277-287
The recent experiments on the chloride-assisted dealkylation of alkylcobalamins by a variety of oxidants (IrCl, AuCl, Fe(H2O)5Cl2+, and PtCl), which are scattered in several previous publications, and their general kinetic characteristics are summarized. The kinetic studies are also extended to include the dealkylations of (methylaquo)?3,5,6-trimethylbenzimidazolylcobamide and protonated base-off ethylcobalamin by IrCl (1.0M Cl?) and by Fe(III) ions at 0.1M Cl?, and the demethylation of (methylaquo)?3,5,6-trimethylbenzimidazolylcobamide by AuCl (1.0M Cl?). This extension is in an effort to substantiate the general mechanism which has been previously proposed for these oxidative dealkylations. The general kinetic characteristics are described in terms of a preassociation of the reactants, followed by a rate-determining electron-transfer process to yield the R-B radical, which then undergoes further reactions to produce the products observed. The overall reactions are discussed within the framework of chlorine-bridging inner sphere electron-transfer reactions. 相似文献
6.
In the radiolysis of water vapor containing small concentrations of cyclohexane, the principal products which account for about 98% of all end products are found to be hydrogen, cyclohexene, and bicyclohexyl. Cyclohexene and bicyclohexyl yields were determined over a range of temperatures (70–200°C), total pressures (50–2400 torr), and total doses (0.15–2.0 Mrad). The disproportionation–combination ratio k/k for c-C6H11 radicals could be determined as 0.56 ± 0.01 from the ratio of cyclohexene to bicyclohexyl yield. By using c-C6D12, the ratio k/k for c-C6D11 radicals is found to be 0.38 ± 0.01. Comparison of the reactivity pattern of C6H11 and C6D11 radicals leads to (k)/(k)/(k/k) = 1.47 ± 0.02. The corresponding values for the reactions of c-C6H11 with c-C6D11 were also determined. 相似文献
7.
The extinction coefficients and the decay kinetics of I and (SCN) have been characterized over the 15–90°C-temperature range. The extinction coefficients of I at 385 and 725 nm were determined to be 10,000 and 2560M?1 cm?1, respectively, based on the extinction coefficient of (SCN) at 475 nm being equal to 7600M?1 cm?1. At these three wavelengths, all extinction coefficients were constant over the temperature range studied. The rate of decay of both I and (SCN) was found to be a function of I? and SCN? concentration, respectively, as well as temperature. 相似文献
8.
Experiments are described in which the kinetics of cathodic hydrogen evolution from the unhydrated H3O+ ion in pure CF3SO H3O+ are compared with those from an aqueous solution of CF3SO3H where the proton is mainly in a fully hydrated state as H9O. From the acid hydrate, which exists mainly as the ionic compound CF3SOH3O+, rates of H2 evolution at Ni, Pt, and Hg electrodes, measured at a given overpotential or expressed as exchange current densities, are between about 3.5 and 20 times slower than those from the same electrolyte in dilute (1.0M) aqueous solution. Allowing for the concentration differences in these two types of system and double-layer effects, the rate constants are between about 9.4 and 216 times smaller for the reaction from H3O+ than from H9O at the above electrodes. The evaluation of apparent heats of activation for H2 evolution from the two types of proton sources allows ratios of real frequency factors to be calculated for discharge from H3O+ and H9O. These data have a bearing on the theoretical conclusions regarding proton discharge mechanisms and show that frequency factor effects can be as important as activation energy differences in determining the rates of proton discharge from different proton sources. The results are discussed in terms of current ideas about electron and proton transfer in electrochemical reactions, the state of hydration of H+, and the role of discharge from paired CF3SO and H3O+ ions. In particular, the molecular mechanics of discharge of the proton from the molecular ion H3O+ can be different from that from the fully hydrated H+ ion where many more HO- vibrational and librational modes can be involved in the process of activation of the H9O entity. 相似文献
9.
The thermal, unimolecular elimination of HF from CH3CF3 was studied by three different groups over the temperature range 1000° to 1800°K. While the reported kinetic parameters varied greatly, it is shown here that these data may be satisfactorily correlated in terms of a four-center transition state. This correlation results in ΔE = 69.2 kcal/mol, and log (k/s?1) = 14.6 – 72.6/θ. These results may then be combined with the kinetics of the chemically activated elimination of HF from CH3CF3 formed by the recombination of methyl and trifluoromethyl radicals. The data from three different laboratories are shown to be in excellent agreement. These data, combined with extant thermal data, yield as a best value DH(CH3? CF3) = 99.6 ± 1.1 kcal/mol. This gives the unexpectedly high value of DH298°(CH3? CF3) = 101.2 ± 1.1 kcal/mol. It is suggested that dipoledipole interactions, primarily in CH3CF3, account for this surprisingly strong C? C bond dissociation energy. These results also yield δH(CH3CF3; g, 298) = ?178.6 ± 1.5 kcal/mol. 相似文献
10.
D. C. McKean 《国际化学动力学杂志》1989,21(6):445-464
An earlier correlation between isolated CH stretching frequencies, v, and experimental CH bond dissociation energies, in hydrocarbons, fluorocarbons, and CHO compounds, is updated. A stabilization energy, E, which reflects only the properties of the radical, is defined by the deviation of a point from the above correlation. E values for a variety of radicals are listed and discussed. In H? C? N and H? C? O compounds E is low or negligible, due to the low v found in these compounds. The conventional definition of ES then represents a serious misnomer, which distracts attention from the probable source of discrepancies between experimental and ab initio values of DH°(C? H), namely, the parent molecules. Stereo electronic effects concerned with the breaking of CH bonds are predicted in a variety of situations. Some experimental determinations of DH°(C? H), viz., in C2H4, HCOOH, CH3CHO, CH3NH2, are considered to be probably in error. Schemes for partitioning energies of atomization into ‘standard’ or ‘intrinsic’ bond energies are criticized. 相似文献
11.
The kinetics of the acqueous-phase reactions of the free radicals ·OH, ·Cl, and SO· with the halogenated acetates, CH2FCOO?, CHF2COO?, CF3COO?, and with CH2ClCOO?, CHCl2COO?, CCl3COO? were investigated. Generally, the reactivity decreases with increasing halogen substitution and is in the order k(·OH) > k(SO·) > k(·Cl), but there is no general relation between the effect on reactivity of chlorine and fluorine substitution. © 1995 John Wiley & Sons, Inc. 相似文献
12.
The thermal decomposition of ethane has been reinvestigated using the single pulse, reflected shock technique. Reflected shock temperatures were corrected for boundary layer-induced nonidealities using the thermal decomposition of cyclohexene as a kinetic standard. The rate constant for the reaction was calculated from the rate of formation of methane under conditions of very low extent of reaction, over a temperature range of 1000–1241 K. Ethane compositions of 1% and 3% in argon at total reaction pressures of 3 and 9 atm were used, and a small pressure dependence of k1 was observed. An RRKM model is described which gives excellent agreement with this and other recent dissociation and recombination rate constant data in light of a recent revision to the thermochemistry of the methyl radical. In the range of 1000–1300 K an RRKM extrapolated k is given by the expression, log k = 17.2 ? 91,000/2.3RT, while at 298 K the calculation gives log k (l/mol sec) = 10.44, where k is calculated from k and the equilibrium constant. 相似文献
13.
The reaction between tris(acetylacetonato)magnanese(III) and hexa(N,N-dimethylformamide)iron(III) perchlorate in acetonitrile proceeds in two stages. The first stage corresponds to the reaction of pentacoordinated Fe(DMF) with Mn(acac)3, and the rate-determining step of the second stage consists mainly in the elimination of a DMF ligand from Fe(DMF) to yield Fe(DMF) which reacts rapidly with the manganese complex. The formation of Fe(DMF) is catalyzed by Mn(acac)3, this catalytic effect being decreased by manganese products. The rate-determining step for the formation of Fe(acac)3 is the transfer of the first acetylacetonate to yield Fe(acac)2+. The final products of iron depend on the ratio of reactant concentrations. With Mn or Fe in excess, Fe(acac)3 or Fe(acac)2+ are mainly produced. 相似文献
14.
Reactions of oxygen atoms with ethylene, propene, and 2-butene were studied at room temperature under discharge flow conditions by resonance fluorescence spectroscopy of O and H atoms at pressures of 0.08 to 12 torr. The measured total rate constants of these reactions are K = (7.8 ± 0.6)·10?13cm3s?1,K = (4.3 ± 0.4) ± 10?12 cm3 s?1, K = (1.4 ± 0.4) · 10?11 cm3 s?1. The branching ratios of H atom elimination channels were measured for reactions of O atoms with ethylene and propene. No H-atom elimination was found for the reaction of O-atoms with 2-butene. A redistribution of reaction O + C2 channels with pressure was found. A mechanism of the O + C2 reaction was proposed and the possibility of its application to other olefins is discussed. On the basis of mechanism the pressure dependence of the total rate constant for reaction O + C2 was predicted and experimentally confirmed in the pressure range 0.08–1.46 torr. 相似文献
15.
A kinetic reinvestigation of the title redox system in aqueous alkaline media at 35°C and an ionic strength of 0.5 mol dm?3 shows that the reaction follows a pseudosecond-order Fe(CN) disappearance. While varying [phenol]0 and [OH?] exhibit a linear influence on the pseudo-second-order rate constant, varying[Fe(CN)]0 and [Fe(CN)]0, initially taken, have a complicated inhibitory effect on the same. The major phenoloxidation products isolated under a chosen condition are 2,2′- and 4,4′- dihydroxydiphenyl. Results are interpreted in terms of a probable mechanism which envisages a reversible formation, by the first one-electron transfer, of a reactive phenoxy radical (PhO˙) which on the second one-electron transfer forms a less reactive ion-pair intermediate (stabilized by the Fe(CN) produced) to decompose rate-determiningly to phenoxonium cation (PhO+) and Fe(CN), the product-formation steps being very rapid and kinetically indistinguishable. 相似文献
16.
A competitive reaction study for two isoelectronic peroxides (peroxodisulfate S2O and peroxodiphosphate P2O) interacting with the free radical ·Clpar;CH3)2OH is described. The radical formation is initiated by photolysis, the amounts of peroxide remaining analyzed volumetrically. It is found that persulfate reacts with the organic radical over 100 times more rapidly than does perphosphate. Mechanistic consequences in relation to previous work are briefly discussed. 相似文献
17.
The substituted thiourea, 4‐methyl‐3‐thiosemicarbazide, was oxidized by iodate in acidic medium. In high acid concentrations and in stoichiometric excess of iodate, the reaction displays an induction period followed by the formation of aqueous iodine. In stoichiometric excess of methylthiosemicarbazide and high acid concentration, the reaction shows a transient formation of aqueous iodine. The stoichiometry of the reaction is: 4IO + 3CH3NHC(S)NHNH2 + 3H2O → 4I− + 3SO + 3CH3NHC(O)NHNH2 + 6H+ (A). Iodine formation is due to the Dushman reaction that produces iodine from iodide formed from the reduction of iodate: IO + 5I− + 6H+ → 3I2(aq) + 3H2O (B). Transient iodine formation is due to the efficient acid catalysis of the Dushman reaction. The iodine produced in process B is consumed by the methylthiosemicarbazide substrate. The direct reaction of iodine and methylthiosemicarbazide was also studied. It has a stoichiometry of 4I2(aq) + CH3NHC(S)NHNH2 + 5H2O → 8I− + SO + CH3NHC(O)NHNH2 + 10H+ (C). The reaction exhibits autoinhibition by iodide and acid. Inhibition by I− is due to the formation of the triiodide species, I, and inhibition by acid is due to the protonation of the sulfur center that deactivates it to further electrophilic attack. In excess iodate conditions, the stoichiometry of the reaction is 8IO + 5CH3NHC(S)NHNH2 + H2O → 4I2 + 5SO + 5CH3NHC(O)NHNH2 + 2H+ (D) that is a linear combination of processes A and B. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 193–203, 2000 相似文献
18.
The kinetics and equilibria of the reaction: have been studied in the temperature range 298–333 K by using the very low pressure reactor (VLPR) technique. Combining the estimated entropy change of reaction (1), ΔS = 8.1 ± 1.0 eu, with the measured ΔG, we find ΔH = 4.2 ± 0.4 kcal/mol; ΔH(CH3CHOC2H5) = ?20.2 kcal/mol, and DH° [Et OCH(Me)-H] = 91.7 ± 0.4 kcal/mol. We find: where θ = 2.3 RT in kcal/mol. It has been shown that the reaction proceeds via a loose transition state and the “contact TS” model calculation gives a very good agreement with the observed value. 相似文献
19.
Kinetics of the complex formation of chromium(III) with alanine in aqueous medium has been studied at 45, 50, and 55°C, pH 3.3–4.4, and μ = 1 M (KNO3). Under pseudo first-order conditions the observed rate constant (kobs) was found to follow the rate equation: Values of the rate parameters (kan, k, KIP, and K) were calculated. Activation parameters for anation rate constants, ΔH≠(kan) = 25 ± 1 kJ mol?1, ΔH≠(k) = 91 ± 3 kJ mol?1, and ΔS≠(kan) = ?244 ± 3 JK?1 mol?1, ΔS≠(k) = ?30 ± 10 JK?1 mol?1 are indicative of an (Ia) mechanism for kan and (Id) mechanism for k routes (‥substrate Cr(H2O) is involved in the k route whereas Cr(H2O)5OH2+ is involved in k′ route). Thermodynamic parameters for ion-pair formation constants are found to be ΔH°(KIP) = 12 ± 1 kJ mol?1, ΔH°(K) = ?13 ± 3 kJ mol?1 and ΔS°(KIP) = 47 ± 2 JK?1 mol?1, and ΔS°(K) = 20 ± 9 JK?1 mol?1. 相似文献
20.
L. A. Margulis I. V. Khudyakov V. A. Kuzmin A. I. Prokof'ev A. I. Yasmenko G. Smets 《国际化学动力学杂志》1985,17(7):735-747
The kinetics of the reversible recombination of the 2-phenyl- (I), 2-p-methoxyphenyl-(II), and 2-p-nitrophenyl-3-oxo-2,3-dihydrobenzothiophene-2-yl (III) radicals have been investigated. Recombination rate constants of R(I–III) have been determined in different solvents (2k1 ~ 109 M?1 s?1). The rate of reaction (I) with R(I–III) decreases with increasing solvent viscosity η. In the toluene-vaseline oil mixture (2 ? η ? 120 cP) the recombination of R(I–III) is molecular mobility limited. The thermodynamic parameters of reaction (I) have been determined: ΔH0 = 20–30 kcal/mol. Activation volumes ΔV for recombination of R(II) have been measured. In n-propanol ΔV is equal to the viscous flow activation volume of the solvent ΔV. In toluene and chloroform ΔV < ΔV. For the last two solvents the activation volumes of the cage reaction have been estimated ΔV = ?(2–3) cm3/mol. Visible-range absorption spectra and ESR spectra have been recorded for R(I–III). The role of cage effect in the reactivity anisotropy averaging of R(I–III) is discussed. The potential of the high-pressure tests for deriving information about the elementary act of a fast bimolecular reaction is considered. 相似文献