The temperature coefficient of the rates in the system Cl + CH4 ⇆ CH3 + HCl,thermochemistry of the methyl radical

The bimolecular rate constant for the title reaction has been measured by very-low-pressure reactor techniques at 233 < T K < 338. The equilibrium constant has also been measured between 253 and 338 K. Our rate constants are in excellent agreement with recent measurements using very different techniques and reaction conditions, and the general agreement probably makes this one of the most accurately measured rateconstants. Transition state models of the reaction rule out a bent TS in favor of a TS with colinear Cl···H···C bonds. The curvature at higher temperatures (>350 K) is quantitatively accounted for by transition state theory analysis. Tunneling is shown not to play a role. The measured values of K₁ allow an experimental value of S° (CH₃) to be fixed to only ±2.4 e.u. However, using known values of S° for all species gives ΔH°_f298(CH₃.) = 35.1 plusmn; 0.1 kcal/mol in excellent agreement with other measured values.     

The decomposition of dimethyl peroxide and the rate constant for CH3O + O2 → CH2O + HO2

The decomposition of dimethyl peroxide (DMP) was studied in the presence and absence of added NO₂ to determine rate constants k₁ and k₂ in the temperature range of 391–432°K: The results reconcile the studies by Takezaki and Takeuchi, Hanst and Calvert, and Batt and McCulloch, giving log k₁(sec^?1) = (15.7 ± 0.5) - (37.1 ± 0.9)/2.3 RT and k₂ ≈ 5 × 10⁴M^?1· sec^?1. The disproportionation/recombination ratio k_7b/k_7a = 0.30 ± 0.05 was also determined: When O₂ was added to DMP mixtures containing NO₂, relative rate constants k₁₂/k_7a were obtained over the temperature range of 396–442°K: A review of literature data produced k_7a = 10^9.8±0.5M^?1·sec^?1, giving log k₁₂(M^?1·sec^?1) = (8.5 ± 1.5) - (4.0 ± 2.8)/2.3 RT, where most of the uncertainty is due to the limited temperature range of the experiments.     

Mechanism of pyrolysis of C2Cl6

Using published data on the kinetics of pyrolysis of C₂Cl₆ and estimated rate parameters for all the involved radical reactions, a mechanism is proposed which accounts quantitatively for all the observations: The steady-state rate law valid for after about 0.1% reaction is and the reaction is verified to proceed through the two parallel stages suggested earlier whose net reaction is A reported induction period obtained from pressure measurements used to follow the rate is shown to be compatible with the endothermicity of reaction A, giving rise to a self-cooling of the gaseous mixture and thus an overall pressure decrease. From the analysis, the bond dissociation energy DH⁰(C₂Cl₅? Cl) is found to be 70.3 ± 1 kcal/mol and ΔH_f300⁰(·C₂Cl₅) = 7.7 ± 1 kcal/mol. The resulting π? bond energy in C₂Cl₄ is 52.5 ± 1 kcal/mol.     

Synthesis of acridines from diphenylamine-2-carboxaldehydes prepared via the mcfadyen-stevens reaction

A general synthesis of acridines has been developed using diphenylamine-2-carboxaldehydes. Diphenylamine-2-carboxylic acids are converted to their p-toluenesulfonylhydrazides which are decomposed using a modified McFadyen-Stevens reaction to yield an aldehyde derivative which affords the acridine upon treatment with mineral acid.     

The kinetics and thermochemistry of the gas phase reaction of cyclopentadiene and iodine. Relevance to the heat of formation of cyclopentadienyl iodide and cyclopentadienyl radical

The rate of the reaction of cyclopentadiene with iodine has been followed spectrophotometrically over the temperature range 171.7° to 276.5°C. The reaction first proceeds almost to the point of equilibrium with cyclopentadienyl iodide and HI, although the final products are fulvalene and HI. Equilibrium constants obtained are those predicted by bond additivity. A third-law value of δH⁰_{f 298} (c-C₅H₅I,g) = 49 kcal/mole is obtained. Rate studies of the reaction up to the iodide equilibrium, yield values for the rate constant . Uncertainty in the Arrhenius parameters, as well as doubts as to the applicability of the usual assumption that E₃ = 1 ± 1 kcal/mole, make difficult an evaluation of total cyclopentadienyl stabilization energy (TSE) from these data. However, the value is probably 15 < TSE < 20.     

Kinetics of the pyrolysis of 1,2-diiodoethylene

The spectrophotometric determination of the rate of pyrolysis of 1,2-diiodoethylene from 305.8 to 435.0° (with additional data on the addition of iodine to acetylene from 198.1 to 331.6°) has resulted in the observation of both a (in part heterogeneous) unimolecular process (A), and an iodine atom catalyzed process (B). For the homogeneous unimolecular process, log (k_A/sec^?1) ≈ 12.5–46/θ would appear to be reasonable, while log (k_B/M^?1 sec^?1) = 11.8–23.9/θ, where θ = 2.303RT in kcal/mole. It is suggested that a donor–acceptor complex intermediate may explain the observed rate constant of process B and analogous reactions in other systems.     

The kinetics of the reaction: Br + C3H6 ⇌ HBr + C3H5

Studies of the reaction of Br + propylene to produce HBr and allyl radical were made using VLPR (Very Low Pressure Reactor) over the range 263–363 K. Apparent bimolecular rate constants k were found to vary in an inverse manner with the initial concentration of bromine atoms introduced into the reactor. Plots of k against [Br] give straight lines whose intercepts were taken to be the true bimolecular, metathesis rate constant k₁. The reaction scheme is where k₂ ? k₁ and k_?1 [HBr] is negligibly small under our conditions. Arrhenius parameters for k₁ were assigned for linear and bent transition states and shown to give excellent fits to the observed intercepts. where θ = 2.303 RT (kcal mol^?1). The dependence of k on [Br] is accounted for in terms of the reactivity of Br* (²P_1/2) produced in the microwave discharge. The activation energy for the metathesis reaction of Br* with propylene is shown to be very small.     

The three-body force,off-shell πN scattering and binding energies in nuclear matter

We re-examine the off-shell πN amplitude occurring in the two-pion exchange three-body force, subject to all of the constraints of current algebra. This amplitude is not dominated by the Δ(1231) isobar; instead, if the σ-term is known, it can be determined from on-shell scattering. The resulting contribution to the binding energy of nuclear matter is small but attractive, varying from 0.2 MeV to 1.5 MeV, corresponding to πN σ-terms of 70 MeV to 40 MeV.     

Mechanism and thermochemistry of oxidation of HCl and HBr at high temperatures. The heat of formation of HO2

Using currently available thermochemical and kinetic data and estimation methods to analyze the thermochemistry and the kinetic parameters of the elementary reactions involved in the oxidation of HCl and HBr, reaction mechanisms are proposed which account for the previously reported reaction products, the rate law, and the kinetic data. For oxidation of HCl, two competitive pathways, the radical initiation by hydrogen abstraction and the fourcenter reaction pathway, were invoked to account for the observations. In the oxidation of HBr one must invoke a fast surface reaction of the type to account for the reaction.