ALBERT

Notes: The previously published equation for the rate of a diffusion-limited bimolecular reaction between chemically asymmetric molecules is studied numerically for the case that one of the reactant molecules is uniform. The results are reproduced quite well by a simple approximate chemical-kinetic steady-state scheme and, in principle, allow estimates of the size of the reactive region and of the activation-controlled rate to be made from the observed dependence of rate on solvent viscosity. The simple scheme is easily generalized to the case of two nonuniform reactants. In general, restriction of reactivity to some fraction of the molecular surface (i.e., a steric factor) must reduce the observable reaction rate, but to an extent which is moderated by the rotational diffusion of the reactant molecules.

Notes: The 147 nm (8.4 eV) photolysis of gaseous C2H5I, n-C3H7I, and sec-C3H7I was investigated in the presence of and absence of HI. The main overall processes are: \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{rcll} {{\rm C}_{\rm 2} {\rm H}_{\rm 5} {\rm I} + h\nu} &\to& {{\rm C}_{\rm 2} {\rm H}_{\rm 4} {\rm + H + I}} & {\phi = 0.75} \\{{\rm n{-} C}_{\rm 3} {\rm H}_{\rm 7} {\rm I} + h\nu }&\to& {{\rm C}_{\rm 3} {\rm H}_{\rm 6} {\rm + H + I}} & {\phi = 0.38} \\& \to&{ {\rm CH}_{\rm 3} +{\rm C}_{\rm 2} {\rm H}_{\rm 4} {\rm + I}} & {\phi = 0.47} \\ {\sec - \,{\rm C}_{\rm 3} {\rm H}_{\rm 7} {\rm I}\, + h\nu} &\to &{{\rm C}_{\rm 3} {\rm H}_{\rm 6} {\rm + H + I}} & {\phi = 0.80} \\ &\to&{ {\rm CH}_{\rm 3} +{\rm C}_{\rm 2} {\rm H}_{\rm 4} {\rm + I}} & {\phi = 0.07} \\\end{array} $$\end{document} These dissociative processes occur mainly as a result of initial cleavage of the weak C—I bond, followed by decomposition of the internally excited alkyl radicals. In all cases, approximately 5-10% of the alkyl radicals thus formed do not undergo dissociation at pressures around 3-7 torr. There is also evidence for the elimination of HI as well as C—C cleavage in the primary dissociation. The former is indicated by deuterium labeling experiments and the formation of cyclopropane (Φ = 0.04) as a product in the photolysis of n-C3H7I. Because the processes listed above provide a constant source of H atoms whose quantum yield can be exactly determined, it was feasible to obtain accurate values for ka/kb: For thermally equilibrated H atoms (300 K), ka/kb is 0.44 ± 0.04, 0.57 ± 0.06, 0.95 ± 0.1, and 0.024 ± 0.01 for C2H5I, n-C3H7I, sec-C3H7I, and C2H5Br, respectively.

Notes: 2,4-Dimethylhexene-l has been decomposed in single-pulse shock tube experiments. Rate expressions for the initial reactions are \documentclass{article}\pagestyle{empty}\begin{document}$$ k(C_4 H_7 - S - C_4 H_9 \to C_4 H_7 .(isobutenyl) + s - C_4 H_9 .) = 10^{15.6} \exp (- 33,200/T)\sec ^{ - 1} $$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$$ k(C_4 H_7 - S - C_4 H_8 \to _i C_4 H_8 + n - C_4 H_8 .) = 10^{12.5} \exp (- 26,900/T)\sec ^{ - 1} $$\end{document} sec-1 at 1.5-5 atm and 1050°K. This leads to ΔH°f300 (CH2 = C(CH3)CH2) = 124 kJ/mol, or an allylic resonance energy of 50 kJ/mol. Rate expressions for the decomposition of the appropriate olefins which yield isobutenyl radicals and methyl, ethyl, isopropyl, n-propyl, t-butyl, and t-amyl radicals, respectively, are presented. The rate expression for the decomposition of isobutenyl radical is \documentclass{article}\pagestyle{empty}\begin{document}$$ k{\rm (C}_{\rm 4} H_7 .(isobutenyl) \to C_3 H_4 (allene) + CH_3 .) = 10^{13.3} \exp (- 2,500/T)\sec ^{ - 1} $$\end{document} (at the beginning of the fall-off region). For the combination of isobutenyl and methyl radicals, the rate constant at 1020°K is \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm k(C}_{\rm 4} H_7 .(isobutenyl) + CH_3 . \to 2 - methylbutene - 1) = 10^{10.3} 1./mol\sec $$\end{document} Combination of this number and the calculated rate expression for 2-methylbutene-1 decomposition gives SC4H7. (1100) = 470 J/mol °K. This yields \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm k(C}H_3 + C_3 H_4 (allene) \to C_4 H_7 .(isobutenyl) = 10^{8.2} \exp (- 2,500/T)l./mol\sec $$\end{document} It is demonstrated that an upper limit for the rate of hydrogen abstraction by isobutenyl from toluene is \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm k(C}_{\rm 4} H_7 . + \emptyset CH_3 \to iC_4 H_8 + \emptyset CH_2 .)\underline \le 10^{8.3} \exp (- 6,000/T)l./mol\sec $$\end{document}

Notes: Pyrolysis of cis-butene-2 under conditions of very low pressure (VLPP) has been studied in the range of 1100-1300°K. The principal products are butadiene and H2, obtained in a unimolecular reaction. A competing reaction to form butene-l accounts for from 10% to 40% of the overall decomposition over the range. Using a «tight» model for the transition state and RRKM theory yields a high-pressure, unimolecular rate constant for the 1,4-H2 elimination of \documentclass{article}\pagestyle{empty}\begin{document}$$ \log \,k\left( {{\rm s}^{ - 1} } \right) = \left( {13.0 \pm 0.6} \right) - {{\left( {65 \pm 2} \right)} \mathord{\left/ {\vphantom {{\left( {65 \pm 2} \right)} \theta }} \right. \kern-\nulldelimiterspace} \theta } $$\end{document} where θ = 2.303RT in kcal/mol. There is some surface reaction of butadiene at these temperatures to yield H2 + nonvolatile residue. Butene-l proceeds to decompose irreversibly to allyl + methyl radicals which have been observed directly. Comparison with related reactions leads to the conclusion that orbital symmetry-forbidden, 1,2-H2 elimination from saturated organic compounds will have activation energies too high to observe.

Notes: The pyrolysis of isobutane was investigated in the ranges of 770° to 855°K and 20 to 150 Torr at up to 4% decomposition. The reaction is homogeneous and strongly self-inhibited. A simple Rice-Herzfeld chain terminated by the recombination of methyl radicals is proposed for the initial, uninhibited reaction. Self-inhibition is due to abstraction of hydrogen atoms from product isobutene giving resonance-stabilized 2-methylallyl radicals which participate in termination reactions. The reaction chains are shown to be long. It is suggested that a previously published rate constant for the initiation reaction (1)\documentclass{article}\pagestyle{empty}\begin{document}$$ i - C_4 H_{10} \to CH_3 + i - C_3 H_7 $$\end{document} is incorrect and the value k1 = 1016.8 exp (-81700 cal mol-1/RT)s-1 is recommended. The values of the rate constants for the reactions (4i) \documentclass{article}\pagestyle{empty}\begin{document}$$ CH_3 + i - C_4 H_{10} \to CH_3 + i - C_4 H_9 $$\end{document} (4t) \documentclass{article}\pagestyle{empty}\begin{document}$$ CH_3 + i - C_4 H_{10} \to CH_4 + t - C_4 H_9 $$\end{document} (8) \documentclass{article}\pagestyle{empty}\begin{document}$$ CH_3 + i - C_4 H_8 \to CH_4 + 2 - methylallyl $$\end{document} are estimated to be \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{4i} = 10^{13.16} \exp (- 16300calmol^{ - 1} /RT)cm^3 mol^{ - 1} s^{ - 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{4t} = 10^{12.51} \exp (- 12900calmol^{ - 1} /RT)cm^3 mol^{ - 1} s^{ - 1} $$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{8} = 10^{14.05} \exp (- 17600calmol^{ - 1} /RT)cm^3 mol^{ - 1} s^{ - 1} $$\end{document} From a recalculation of previously published data on the pyrolysis of isobutane at lower temperatures and higher pressures, the value k11c, = 109.6 cm3 mol-1 s-1 is obtained for the rate constant of recombination of t-butyl. A calculation which is independent of any assumed rate constants or thermochemistry shows that the predominant chain termination reaction is the recombination of two methyl radicals in the conditions of the present work and the recombination of two t-butyl radicals in those of our previous study at lower temperatures and higher pressures.

Notes: The gas phase thermal isomerization of 1,2-bis(trimethylsiloxy)cyclobutene has been studied in the temperature range 172°-204°C. The reaction is homogeneous, kinetically first order, and yields 2,3-bis(trimethylsiloxy)buta-1,3-diene as the only product. The rate constants fit the Arrhenius equation \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {k = 10^{13.509 \pm 0.120} \exp \left( {{{ - 148,920 \pm 1060\,{\rm J}\,{\rm mole}^{ - 1} } \mathord{\left/ {\vphantom {{ - 148,920 \pm 1060\,{\rm J}\,{\rm mole}^{ - 1} } {RT}}} \right. \kern-\nulldelimiterspace} {RT}}} \right)\sec ^{ - 1} } \hfill \\ {\left[ {k = 10^{13.509 \pm 0.120} \exp \left( {{{ - 35,590 \pm 250\,{\rm cal mole}^{ - 1} } \mathord{\left/ {\vphantom {{ - 35,590 \pm 250\,{\rm cal mole}^{ - 1} } {RT}}} \right. \kern-\nulldelimiterspace} {RT}}} \right)\sec ^{ - 1} } \right]} \hfill \\ \end{array}$$\end{document} These results, taken with those obtained previously, demonstrate the insensitivity of the kinetics of the reaction to the nature of the groups substituted on the 1- and/or 2-positions of the cyclobutene ring.

Notes: A simple model involving random displacements of particles in a cubic lattice is used to evaluate the importance of primary and secondary recombination in cage processes and leads to estimates of the lifetime of cage pehnomena. However, it is pointed out that all such models, and treatments which attempt to relate processes at the molecular level with bulk viscosity or diffusion constants, are inherently qualitative since they ignore the important correlation between motions of neighboring molecules.

Notes: A critical examination has been made of some aspects of the thermal decomposition of ethane and the reverse recombination reaction. The experimental Arrhenius A-factors for ethane are, in general, smaller than those which are calculated from thermodynamic quantities together with the observed rate constants for methyl recombination. Theoretical calculations also illustrate a discrepancy between the experimental work on recombination and decomposition. The experimental shapes of k/kα falloff curves and the pressure region of falloff are compared with the predictions of RRKM theory for various models.

Notes: The rate constant for the combination of 1,1-dichloro-2,2,2-trifluoroethyl radicals in the gas phase has been measured by applying the rotating sector technique to the 1,1,1-trichloro-2,2,2-trifluoroethane-cyclohexane photochemical system. The combination rate constant, k5, was found to be 6.6 × 1012 cc mole-1 sec-1. Arrhenius parameters for the reaction, are given by the expression log k4 = 11.81 - (9700/2.3RT).

Notes: The rate constant for the combination of trichloromethyl radicals in the gas phase has been measured by applying the rotating sector technique to the gas phase carbon tetrachloride-cyclohexane photochemical system. A temperature-independent rate constant, k5, of 3.9 ± 1.0 × 1012 cc mole-1 sec-1 was found. Arrhenius parameters for the reaction \documentclass{article}\pagestyle{empty}\begin{document}$${\rm CCl}_{\rm 3} + c - {\rm C}_{\rm 6} {\rm H}_{{\rm 12}} \mathop {\hbox to 30pt{\rightarrowfill}}\limits^{k_4 } {\rm CHCl}_{\rm 3} + c - {\rm C}_{\rm 6} {\rm H}_{{\rm 11}} $$\end{document} were found to be given by the expression log k4 = 11.79 - (10,700/2.3 RT).

Notes: The reaction of OH with acetylene was studied in a discharge flow system at room temperature. OH was generated by the reaction of atomic hydrogen with NO2 and was monitored throughout the reaction using ESR spectroscopy. Mass-spectrometric analysis of the reaction products yielded the following results: (1) less than 3 molecules of OH were consumed, and less than 2 molecules of H2O were formed for every molecule of acetylene that reacted; (2) CO was identified as the major carbon-containing product; (3) NO, formed in the generation of OH, reacted with a reaction intermediate to give among other products N2O. These observations placed severe limitations on the choice of a reaction mechanism. A mechanism containing the reaction OH + C2H2 → HC2O + H2 better accounted for the experimental results than one involving the abstraction reaction OH + C2H2 → C2H + H2O. The rate constant for the initial reaction was measured as 1.9 ± 0.6 × 10-13 cm3 molecule-1 sec-1.

Notes: The addition of methyl radicals to hexafluoropropylene has been studied over the temperature range 81°-203°C using a mass-balance technique involving the photolysis of biacetyl in the presence of hexafluoropropylene-isobutane mixtures. For the reaction \documentclass{article}\pagestyle{empty}\begin{document}$${\rm CH}_{\rm 3} + {\rm C}_3 {\rm F}_6 \to {\rm CH}_3 {\rm C}_{\rm 3} {\rm F}_6$$\end{document} the rate constant is given by the equation \documentclass{article}\pagestyle{empty}\begin{document}$${\rm log}k{\rm (in mole}^{- {\rm 1}} {\rm cm}^{\rm 3} {\rm sec}^{- {\rm 1}} {\rm) = (12}{\rm .04} \pm {\rm 0}{\rm .06)} - \frac{{6200 \pm 110}}{{2.303RT}}$$\end{document} The result suggests that methyl radicals are very unselective in their behavior reacting with tetrafluoroethylene and hexafluoropropylene at similar rates. This is in marked contrast to the behavior of oxygen atoms with these olefins.

Notes: The rate constants for the replacement of water from the inner-coordination shell of Co(NH3)5OH23+, I, by dimethyl sulfoxide (DMSO) as DMSO gradually replaced water in the solvation shell of I were found to approach, and finally equal, the water-exchange rate constant of I in aqueous media in accordance with expectation for a dissociative mechanism. Also the rate constants for the replacement of DMSO from the innercoordination shell of Co(NH3)5DMSO3+, II, by water as water replaced DMSO in the solvation shell of II were found to approach, and approximately equal, the DMSO-exchange rate constant for II in liquid DMSO in accordance with expectation for a dissociative mechanism.The DMSO-exchange rate constant for II in liquid DMSO was determined and found to be equal to (3.6 ± 0.8) × 10-4 sec-1 at 45°C.The dissociation quotient, [II] [NO3-]/[Co(NH3)5NO32+], was found to be equal to 0.28 ± 0.11 M at 45°C by NMR methods. The pseudo first-order rate constants for anation of II by NO3- and the solvation of Co(NH3)5NO3 2+ by DMSO were determined at various temperatures.

Notes: The photochemistry of p-fluoranil in dioxane was studied by electron spin resonance (ESR) and the ESR-rotating sector technique. The transient photoradical is identified as the p-tetrafluorobenzosemiquinone neutral radical with a hyperfine splitting of 1.1 gauss for the hydroxy proton and the fluorine hyperfine splittings of 3.8 and 14.1 gauss for the meta and ortho fluorines, respectively. The radicals decayed by self-disproportionation with a second-order rate constant at room temperature of approximately 3.2 × 109M-1s-1. The activation energy of the decay process is found to be about 2.4 ± 0.4 kcal/mole.

Notes: The process of acetal hydrolysis is analyzed in terms of the competing steps of proton transfer and heavy atom reorganization. The results of this analysis are portrayed in a series of three-dimensional reaction coordinate diagrams. The observed pathway of hydrolysis (A-1, general acid catalyzed, or spontaneous) is shown to depend on the energy of the various possible intermediates in these reactions.

Notes: First-order rate constants for formation of cyclohexanone and 2-cyclohexen-1-ol from 1,2-epoxycyclohexane and 1,2-epoxycyclohexane-3,3,6,6-d4 have been determined over the temperature range of 677-746°K. The observed kinetic isotope effects are used in an attempt to determine the mechanism for formation of products. A distinction between a biradical and a concerted mechanism for the alcohol formation could not be made. However, if a common biradical is the precursor of both cyclohexanone and 2-cyclohexenl-ol then the rate of ring closure of this biradical must be much faster than the rates of hydrogen transfer to give the ketone and the alcohol.

Notes: Translation-vibration (T-V) and vibration-vibration (V-V) energy transfer processes in the N2-CO2 system were investigated using classical trajectory techniques. Two empirical interaction potentials were employed. One is comprised of independent, atom-atom Morse-type functions operating between nonbonded atoms. The other included these atom-atom Morse functions plus Coulombic terms to account for the quadrupole-quadrupole intertion. Both interaction potentials led to similar T-V results. However, the result that CO2(v3) is excited ∼103 times more efficiently than N2(v = 1) was obtained, which is at variance with existing analytical theories of T-V energy transfer employing purely repulsive short-range potentials. Different V-V energy transfer probabilities were obtained from the two interaction potentials. The most important finding is that only when electrostatic orientation effects are combined with short-range repulsive interactions is the near-resonant \documentclass{article}\pagestyle{empty}\begin{document}$${\rm N}_{\rm 2} {\rm (}v = {\rm 1)} + {\rm CO}_{\rm 2} {\rm (000)} \to {\rm N}_{\rm 2} {\rm (}v = {\rm 0)} + {\rm CO}_{\rm 2} {\rm (001)}$$\end{document} V-V transfer found to be the dominant energy transfer path. This interaction potential also crudely accounts for the negative temperature dependence observed for this near-resonant V-V transfer at low temperatures (300-1000°K).

Notes: Vibrationally excited pentyl-1, -2, and -3 radicals were formed selectively by the addition of thermal H atoms to the various pentene isomers with approximately 47 kcal/mole of vibrational energy. Decomposition products other than those expected, along with their pressure dependences, support the fact that either 1,2 or 1,3 hydrogen migrations with either a 3- or 4-member cyclic transition state is occurring with a ka of approximately 3 × 105 or 6 × 105 sec-1. A corresponding critical energy of 33 or 31 kcal/mole is found.

Notes: 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: TextOlefin\documentclass{article}\pagestyle{empty}\begin{document}$$\frac{{A_{{\rm olefin}} }}{{A_{{\rm 2TFMP}} }}$$\end{document}ΔERef\documentclass{article}\pagestyle{empty}\begin{document}$$\frac{{A_{{\rm olefin}} }}{{A_{{\rm C}_{\rm 2} {\rm H}_{\rm 4} } }}$$\end{document}ΔEC2H4CH2—CH21.10-1.18(1.0)(0)CH2—CHF1.030.840.942.02CH2—CF20.711.490.652.67CHF—CHF (cis-)1.231.921.123.10CHF—CHF (trans-)1.400.791.271.97CF2—CHF1.060.000.961.22CF2—CF20.86-3.220.78-2.04ΔERef = Eolefin - E2TFMP and ΔEC2H4 = Eolefin - EC2H4. Units are kJ/mole.The results are compared with corresponding data for other atoms and radicals, and discussed in terms of the electronic changes produced in the double bond by fluorine substitution, and in relation to the nature of the transition state.

Notes: Nucleophilic substitution reactions in the alkyl halides, RX + Y- → RY + X-, proceeding in polar media are considered on the basis of the theory presented in Part A. It is shown that the solvent reorganization energy is the main part of the activation energy for this processes. According to calculations performed, the values of the solvent reorganization energy equal ∼2.5-3 eV for H2O and ∼ 1.8-2.3 eV for acetone. From experimental data on the kinetic isotope effect, an estimate for the splitting of nonadiabatic terms and for the slope of the potential curve v′ of the intermolecular interaction between halide ion and methyl halide near transition configuration is made. Further, the parameter v′ is used for calculating the activation entropy of substitution reactions in the methyl halides. Theoretical activation energies and activation entropies agree with experimental values. In the framework of theory presented an interpretation of change of Ea and the preexponential factor with the type of alkyl halide is given.

Notes: Predictions of the “redox” and “complex” schemes for the Fe3+ catalyzed decomposition of H2O2 have been compared with published and new experimental data by numerical integratior of the appropriate complete sets of differential equations. Apparent discrepancies for the redox scheme at high Fe3+/H2O2 ratios are shown to disappear in the complete treatment, and inconsistencies of the complex scheme with both kinetic data and spectroscopic measurements are pointed out.

Notes: The photochemistry of 1,1,1-trifluoromethylazomethane has been partially characterized. The quantum yield for N2 formation from photolysis at 366 nm and room temperature was unity at low pressure and decreased to 0.5 at 630 torr. At room temperature the principal products were C2H6, C2F6, CH3CF3 (or CH2CF2 + HF at reduced pressures), plus substituted hydrazines, which mainly arise from addition of CF3 to the parent followed by combination of these radicals with CH3 or CF3. These fluorinated methyl hydrazine products detract from the general utility of CF3-N2-R compounds as sources for simultaneous study of the chemistry of CF3 and R radicals. At room temperature the hydrazine products accounted for more than 50% of the total yield; however, these products can be reduced by lowering the temperature and at 195°K their yields are negligible. The quantum yield for intramolecular (direct) formation of CH3CF3 + N2 was shown to be ≤0.002.

Notes: The addition of propene to cyclohexa-1,3-diene has been studied between 512 and 638°K at pressures between 70 and 640 torr. The products are endo- and exo-5-methylbicyclo [2.2.2] oct-2-ene, and their formations are second order. The rate constants (in 1./mole-sec) are given by \documentclass{article}\pagestyle{empty}\begin{document}$$\log _{10} k_{{\rm endo}} = - (26070 \pm 80)/4.576T + (5.74 \pm 0.03)$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$\log _{10} k_{{\rm exo}} = - (30090 \pm 80)/4.576T + (6.66 \pm 0.03)$$\end{document} The results are discussed in terms of a biradical mechanism.

Notes: The photolysis of CD2CO at 313 nm in the presence of neopentane was carried out over the temperature range 576-706 K. Analysis of the products and isotopic analysis of the methanes demonstrate abstraction of H from neopentane and D from CD2CO by methylene. The relative kinetics of abstraction of H and D have been measured over the temperature range, and the absolute value for the collision yield of the abstraction of H from neopentane by CD2 at 653 K has been been estimated to be about 1.5 × 1011 mole-1 cm3 sec-1, a value 103 times larger than the corresponding reaction of CH3.

Notes: Hydrogen abstraction from boron trimethyl has been studied using the abstracting radicals CF3 and CD3, from the photolysis of the corresponding ketones over the temperature range of 150° to 300°C. The following Arrhenius parameters were obtained: \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{l} {\rm (CD}_{\rm 3} {\rm + BME}_{\rm 3} {\rm); log }A{\rm = 11}{\rm .8, }E{\rm = 9}{\rm .98 kcal/mole} \\ {\rm (CF}_{\rm 3} {\rm + BMe}_{\rm 3} {\rm); log }A{\rm = 11}{\rm .6, }E{\rm = 6}{\rm .59 kcal/mole} \\ \end{array}$$\end{document} The difference ECD3 - ECF3 in the case of BMe3 is considered due, in part, to polar effects. An exchange reaction is proposed for both CF3 and CD3 in collisions with BMe3: \documentclass{article}\pagestyle{empty}\begin{document}$${\rm R} + {\rm B}({\rm Me})_3 \to {\rm Me} + {\rm RBMe}_2$$\end{document} Radical combination of CF3 and CH2BMe2 leads to a hot molecule which undergoes a β-fluoro rearrangement elimination process, or a stabilized molecule which can thermally decompose:

Notes: The mercury-photosensitized oxidation of CO was studied at 275°C over a wide range of [O2]/[CO] ratios in the absence and presence of the oxygen atom scavenger 2-trifluoromethylpropene (TMP) and at 25°C at low [O2]/[CO] ratios in the presence of TMP. By following the quantum yield of CO2 production, Φ {CO2}, as a function of the [O2]/[CO] ratio, the reactions of vibrationally excited CO (v υ 9) and electronically excited O2, probably in the c1Σ-u state, were studied. At low [O2]/[CO] ratios the predominant reactions are of vibrationally excited CO (v υ 9). Relative rate constants for chemical reaction versus deactivation of CO (v υ 9) were obtained. At higher [O2]/[CO] ratios, the principal reactions are of electronically excited O2. Relative rate constants for chemical reactions and deactivation of this electronically excited O2 with CO, O2, and TMP were obtained. From the effect of total pressure on Φ {CO2}, it is proposed that an intermediate CO3 is formed in the reaction of electronically excited O2 with CO.

Notes: Rate constants for the tri-n-butyltin radical (Sn ·) induced decomposition of a number of peroxides have been measured in benzene at 10°C. The values range from ∼100 M-1 sec-1 for di-t-butyl peroxide to 2.6 × 107 M-1 sec-1 for di-t-butyl diperoxyisophthalate. The majority of the peroxides, including diethyl peroxide, diacetyl peroxide, and t-butyl peracetate, have rate constants of ∼105 M-1 sec-1. It is shown that di-n-alkyl disulfides are ten times as reactive toward Sn · as di-n-alkyl peroxides, although the exothermicities of these reactions are ∼15 and ∼39 kcal/mole, respectively. The enhanced reactivity of the disulfides is attributed to the easier formation of an intermediate or transition state with 9 electrons around sulfur, compared with an analogous species with 9 electrons around oxygen.The following bond strengths (kcal/mole) have been estimated: D[Sn—OR] = 77; D[Sn—H] = 82; D[Sn—SR] = 83; and D[Sn—OC(O)R] = 86, where R = alkyl. Rate constants for reaction of Sn · with some benzyl esters have also been measured. It has been found that t-butoxy radicals can add to benzene and abstract hydrogen from benzene at ambient temperatures.

Notes: The orientation of addition of H atoms to the asymmetric olefins propylene, butene-1, and isobutene has been determined as a function of atom concentration, olefin concentration, hydrogen pressure, total pressure, and olefin conversion. Conditions have been determined for which complicating secondary processes are believed to be unimportant. The percentage of nonterminal addition is 5.7, 5.7, and 0.48 for propylene, butene-1, and isobutene, respectively. From these data activation energy differences between nonterminal and terminal addition of 1.7 and 3.2 kcal/mole for the linear olefins and isobutene, respectively, may be calculated. For D atom addition to propylene, a small isotope effect was observed, nonterminal addition being 5.4%. These observations are consistent with a predominantly free radical or electroneutral character for H atoms.

Notes: In 1958, Bartlett and Hiatt [1] suggested that the number of bonds which are rotationally “frozen” at the transition state for decomposition of peresters can be determined from the magnitude of the values of ΔH

Notes: The kinetics of the gas phase decomposition of 1,2-epoxy-2-methylpropane has been studied over the temperature range 377°-436°C at pressures between 5.3 and 61.6 torr. Isomerization reactions to give isobutyraldehyde, isopropenyl methyl ether, and 2-methyl-prop-2-en-l-ol account for over 95% of the epoxide decomposition. These isomerizations are homogeneous first-order, nonradical processes: \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{l} k({\rm isobutyraldehyde)} = {\rm 10}^{{\rm 13}{\rm .32} \pm {\rm 0}{\rm .18}} \exp (- 52720 \pm 570/1.987T)\sec ^{- 1} \\ {\rm}k({\rm isopropenyl methyl ether)} = {\rm 10}^{{\rm 13}{\rm .55} \pm {\rm 0}{\rm .47}} \exp (- 56140 \pm 1460/1.987T)\sec ^{- 1} \\ {\rm}k({\rm 2 - methyl - prop - 2 - en - l - ol)} = {\rm 10}^{{\rm 11}{\rm .53} \pm {\rm 0}{\rm .67}} \exp (- 49680 \pm 2080/1.987T)\sec ^{- 1} \\ \end{array}$$\end{document}

Notes: The kinetics of the gas phase isomerization of 1-chloro-4-bromobicyclo[2.2.0]hexane to 2-chloro-5-bromohexa-1,5-diene have been measured in a static system over the temperature range of 135-215°C, with a variation in the total pressure from 0.6 to 400 torr. For these conditions the rate constants are well represented by the Arrhenius equation: \documentclass{article}\pagestyle{empty}\begin{document}$${\rm log (}k{\rm /sec}^{ - {\rm 1}} {\rm)} = {\rm (13}{\rm .2} \pm {\rm 0}{\rm .2)} - (34.5 \pm 0.4)/\theta$$\end{document} where θ = 2.303RT kcal/mole. Transition state estimates for the biradical mechanism for the isomerization of bicyclo[2.2.0]hexanes are shown to be in good agreement with these Arrhenius parameters. By comparison of the activation energy with that for the isomerization of bicyclo[2.2.0]hexane and 1,4-dichlorobicyclo[2.2.0]hexane, the radical stabilization energy of an α-bromine atom is shown to be 1.0 ± 1.8 kcal/mole. Rates are also reported in the liquid phase at temperatures of 155°C and 175°C with diphenyl ether, nitrobenzene, and dimethylsulfoxide as solvents. The observed rate constants are all faster (by a factor of 1.1-1.7) than those measured in the gas phase and display no correlation between rate and solvent polarity.

Notes: Quantum yields of the triplet sulfur dioxide (3SO2)-sensitized phosphoresence (Φsens) in biacetyl (Ac2) have been determined in experiments over a wide range of pressures of SO2 and Ac2. Excited singlet sulfur dioxide (1SO2) was generated using 2650-Å and 28757hyphen;Å light. The values of Φsens were dependent on the [SO2]/[Ac2] ratio, as anticpated theoretically. However, in runs at a fixed [SO2]/[Ac2] ratio, the measured Φsens values were dependent on the total pressure. This theoretically unexpected effect is probably largely the result of biacetyl triplet diffusion with deactivation at the cell wall. Treatment of the quantum yield data in terms of the complete mechanism gave new estimates of the following rate functions: 1SO2 + SO2 → (2SO2) (1), 1SO2 + SO2 → 3SO2 + SO2 (2), k2/(k1 + k2) = 0.082 ± 0.003 (2650 Å), 0.095 ± 0.005 (2875 Å) 3SO2 + Ac2 → SO2 + 3Ac2 (9a), 3SO2 + Ac2 → SO2 + Ac2 (9b), k9a + k9b = (8.4 ± 2.1) × 1010 (2650 Å), (8.1 ± 3.0) × 1010 l./mole-sec (2875 Å) 3SO2 → SO2 + hvp (6), k6 = (7.3 ± 1.3) × 101 sec-1.

Notes: Values of the rate constants for allyl-radical abstraction from toluene and allyl-radical recombination have been recalculated in the light of recent data on butene-1 decomposition. The rate of recombination is in good agreement with that found by Van den Bergh and Callear [13] and the cross-combination ratio for the allyl + methyl system has a “normal” value of almost 4. It is concluded that allyl radicals behave like alkyl radicals in respect of their rates of reaction with other radicals.

Notes: Absolute rate constants for the reaction of S(3P) with ethylene were measured over an ethylene concentration range of 7, a total pressure of 50 to 400 torr, and a flash intensity range of 10. At 298°K, the bimolecular rate constant was found to be invariant over this range of variables and had a measured value of 4.96 × 10-13 cm3 molec-1 s-1. Over the temperature range of 218° to 442°K, the rate data could be fit to a simple Arrhenius equation of the form \documentclass{article}\pagestyle{empty}\begin{document}$$k_1 = (7.13 \pm 0.74) \times 10^{ - 12} {\rm exp}\left({\frac{{{\rm - 1}{\rm .58} \pm {\rm 0}{\rm .08 kcal/mole}}}{{RT}}} \right)$$\end{document} Units are cm3 molec-1 s-1. The dependence of the measured value of k1 on the concentration of the reaction product ethylene episulfide is discussed.

Notes: The gas phase iodination of cyclobutane was studied spectrophotometrically in a static system over the temperature range 589° to 662°K. The early stage of the reaction was found to correspond to the general mechanism \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{l} {\rm RH} + {\rm I} \cdot \mathop {{\rm \rightleftharpoons}}\limits^1 {\rm R} \cdot + {\rm HI} \\ {\rm R} \cdot + {\rm I}_{\rm 2} \mathop {{\rm \rightleftharpoons}}\limits^2 {\rm R} - {\rm I} + {\rm I} \cdot \\ \end{array}$$\end{document} where the Arrenius parameters describing k1 are given by log k1/M-1 sec-1 = 11.66 ± 0.11 - 26.83 ± .31/θ, θ = 2.303RT in kcal/mole. The measured value of E1, together with the fact that E-1 = 1 ± 1 kcal/mole, provides ΔHf,2980(c-C4H7.) = 51.14 ± 1.0 kcal/mole, and the corresponding bond dissociation energy, D(c-C4H7—H) = 96.8 ± 1.0 kcal/mole. A bond dissociation energy of 1.8 kcal/mole higher than that for a normal secondary C—H bond corresponds to one half of the extra strain energy in cyclobutene compared to cyclobutane and is in excellent agreement with the recent value of Whittle, determined in a completely different system. Estimates of ΔHf0 and entropy of cyclobutyl iodide are in very good agreement with the equilibrium constant K12 deduced from the kinetic data. Also in good agreement with estimates of Arrhenius parameters is the rate of HI elimination from cyclobutyl iodide.

Notes: The method of chemical difference was utilized to accurately determine the relative importance of all the reaction steps in the direct photolysis of N2O at 2139 Å (25° and 250°C) and 1849 Å (25° C), as well as in the Hg6(1P1)-sensitized photolysis of N2O at 1849 Å (25°C). In all cases, the primary process is predominantly, if not exclusively, \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {{\rm (1)}} & {{\rm N}_{\rm 2} {\rm O} + hv{\rm or H}_{\rm g} 6(^1 P_1) \to {\rm N}_{\rm 2} + {\rm O(}^{\rm 1} D{\rm)}} \\\end{array}$$\end{document} Experiments with trace amounts of C3H6 added showed a slight, but not significant, difference in product ratios (N2 and O2). From these experiments the quantum yield of O(3P) from all possible sources was estimated as 0.02 ± 0.02. Experiments with excess N2 at 1849 Å indicated that O(1S) was not produced in the direct photolysis. The O(1S) yield is probably zero, and certainly 〈0.05. The O(1D) atom can react with N2O via \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{l} \begin{array}{*{20}c} {{\rm (2)}} & {{\rm O(}^{\rm 1} D{\rm)} + {\rm N}_{\rm 2} {\rm O} \to {\rm N}_{\rm 2} + {\rm O}_2 } \\\end{array} \\ \begin{array}{*{20}c} {{\rm (3)}} & {{\rm O(}^{\rm 1} D{\rm)} + {\rm N}_{\rm 2} {\rm O} \to 2{\rm NO}} \\\end{array} \\ \end{array}$$\end{document} The ratio k2/k3 was found to be 0.69 ± 0.05 in all cases. When combined with other data from our laboratory, the average value is 0.65 ± 0.07. This represents the value for translationally energetic O(1D) atoms. When excess He was added to remove the excess translational energy, k2/k3 rose to 0.83 ± 0.06, which is in reasonable agreement with the value of 1.01 ± 0.06 found in another laboratory. We conclude that for O(1D) atoms with no excess thermal energy, k2/k3 = 0.90 ± 0.10.

Notes: The reaction of NO2 with C2F4 was studied at 30°, 68°, 114°, and 157°C by in situ monitoring the infrared absorption bands of the products. The major primary products of the reaction are O2NCF2CFO and FNO. Smaller amounts of CF2O (and presumably NO) are also produced. There was no evidence for other primary products, though they may have been produced in minor amounts. The rate laws for the production of both O2NCF2CFO and CF2O are first order in both [NO2] and [C2F4]. CF2O production is at least partly heterogeneous as demonstrated by packing the quartz reaction vessel with Pyrex beads and by using a Monel cell. The homogeneous rate constant obtained from the high-temperature results gives a rate constant of 3.4 × 108 exp (minus;17000/RT) M-1sec-1 for CF2O production. Actually these Arrhenius parameters represent lower limits, since the heterogeneous reaction may still be playing a significant role. The production rate of O2NCF2CFO is not much affected by changing the nature of the surface or the surface to volume ratio. However the reaction may be heterogeneous, since the rate constant for its formation of 1.3 × 104 e×p (-7500/RT) M-1sec-1 has an abnormally low pree×ponential factor. E×periments in the presence of NO indicate that the mechanism for O2NCF2CFO formatlon is \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{l} \begin{array}{*{20}c} {(11)} & {{\rm NO}_{\rm 2} + {\rm C}_{\rm 2} {\rm F}_{\rm 4} \to {\rm O}_{\rm 2} {\rm NCF}_{\rm 2} {\rm CF}_{\rm 2} } \\ \end{array} \\ \begin{array}{*{20}c} {(12)} & {{\rm O}_{\rm 2} + {\rm NCF}_{\rm 2} {\rm CF}_{\rm 2} + {\rm NO}_{\rm 2} \to {\rm O}_{\rm 2} {\rm NCF}_{\rm 2} {\rm CFO} + {\rm FNO}} \\ \end{array} \\ \end{array}$$\end{document} The intermediate can also react with NO: \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {(13)} & {{\rm O}_{\rm 2} {\rm NCF}_{\rm 2} {\rm CF}_{\rm 2} + {\rm NO} \to {\rm O}_{\rm 2} {\rm NCF}_{\rm 2} {\rm CF}_{\rm 2} {\rm NO}} \\ \end{array}$$\end{document} with k13/k12 = 1.3.

Notes: Instances of high reactivity (as signaled by a positive Brönsted deviation) by nucleophiles bearing one or more unshared pairs of electrons on an atom adjacent to the nucleophilic center (the alpha effect) are surveyed in the context of possible explanations for this phenomenon. No single cause appears to account satisfactorily for all the data. However, four factors (ground-state destabilization of the nucleophile, transition-state stabilization, solvent effect differences for alpha and nonalpha nucleophiles, and product stability) may be involved in contributory roles. The response to proton basicity of a substrate is probably not related to its susceptibility to the alpha effect. Carbon electrophiles seem to be receptive to the alpha effect in the order digonal 〉 trigonal 〉 tetrahedral. The inconsistent behavior of alpha nucleophiles makes the prediction of alpha effects rather risky and confirms the complicated nature of nucleophilic substitutions.

Notes: At temperatures of 356-425°C and pressures of 15-60 Torr, cyclopropylamine reacts to give an equimolar mixture of ammonia and N-propylidenecyclopropylamine as the initial product. The reaction is first order, homogeneous, and unaffected by the presence of radical inhibitors, and thus proceeds by an initial rate-determining unimolecular isomerization to give a reactive intermediate, which then reacts with a further molecule of cyclopropylamine to give the observed products. Reaction in the presence of added aliphatic amines gives other imines in addition, and the nature of these indicates that the intermediate is propenylamine or its tautomer propylideneamine:

Notes: Study of n-butane pyrolysis at high temperature in a flow system allows measurement of the sum of the rate constants of the initiation reactions \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{l} \begin{array}{*{20}c} {(1)} & {{\rm C}_{\rm 4} {\rm H}_{{\rm 10}} \to {\rm 2C}_{\rm 2} {\rm H}_{\rm 5} ^{\rm .} } \\ \end{array} \\ \begin{array}{*{20}c} {(2)} & {{\rm C}_{\rm 4} {\rm H}_{{\rm 10}} \to {\rm CH}_{\rm 3} ^{\rm .} } \\ \end{array} + {\rm C}_{\rm 3} {\rm H}_{\rm 7} ^{\rm .} \\ \end{array}$$\end{document} and of the Arrhenius parameters of the reactions \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{l} \begin{array}{*{20}c} {(3)} & {{\rm CH}_{\rm 3} ^{\rm .} + {\rm C}_{\rm 4} {\rm H}_{{\rm 10}} \to {\rm CH}_{\rm 4} + {\rm C}_{\rm 4} {\rm H}_{\rm 9} ^{\rm .} } \\ \end{array} \\ \begin{array}{*{20}c} {(4)} & {{\rm C}_{\rm 2} {\rm H}_{\rm 5} ^{\rm .} + {\rm C}_{\rm 4} {\rm H}_{{\rm 10}} \to {\rm C}_{\rm 2} {\rm H}_{\rm 6} } \\ \end{array} + {\rm C}_{\rm 4} {\rm H}_{\rm 9} ^{\rm .} \\ \end{array}$$\end{document} Established data for k1/k2 allow estimation of k1 for 951°K and this, with recent thermochemical data, yields the result log k-1 (l.mole s-1) = 8.5, in remarkable agreement with a recent measurement [20] but over si×ty times smaller than conventional assumption. The product k3k4 (l.2mole-2s-2) is found to be associated with the Arrhenius parameters log (A3A4) = 21.90 ± 0.6 and (E3 + E4) = 38.3 ± 2.7 kcal/mole. These values are much higher than would be e×pected on the basis of low temperature estimates. Independent evaluation gives log A4 = 10.5 ± 0.4 (l.mole-1s-1) and E4 = 20.1 ± 1.7 kcal/mole, hence log A3 = 11.4 ± 0.8 (l.mole-1s-1) and E3 = 18.2 ± 3.2 kcal/mole. These values are shown to be entirely consistent with a wide range of results from pyrolytic studies, and it is argued that they further confirm the view that Arrhenius plots for alkyl radical-alkane metathetical reactions are strongly curved, in part due to tunneling and, appreciably, to other as yet unidentified effects. Since there is published evidence that metathetical reactions involving hydrogen atoms show even greater curvature, it is suggested that this may be a characteristic of many metathetical reactions.

Notes: The photolysis of formamide vapor at 2062 Å has been studied in a flow system with results essentially similar to those obtained previously under static conditions and higher conversions. The rotating-sector technique has been applied to the radical-chain decomposition of formamide under conditions (305°C, 11.5 torr) such that decomposition of the carbamyl (NH2CO) radical was rate controlling, so that [NH2CO] ≫ [NH2]. A rate constant of (3.1 ± 1.0) × 1010(M·sec)-1 was obtained for bimolecular chain termination by carbamyl radicals. A concurrent first-order radical loss, probably at the surface, was taken into account by the treatment described by Shepp. Both oxamide and HNCO were tentatively identified as termination products, suggesting the occurrence of both combination and disproportionation,\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} 2{\rm NH}_2 {\rm CO} \to {\rm NH}_{\rm 2} {\rm CO} \cdot {\rm CO} \cdot {\rm NH}_{\rm 2} \\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, \to {\rm HNCO + NH}_{\rm 2} {\rm CHO} \\ \end{array} $$\end{document} but quantitative estimates of the relative rates were not possible. From the rate constant for chain termination, and relative rate constants obtained previously, Arrhenius parameters A∞ = (5.9 ± 2.0) × 1012 sec-1 and A0 = (1.04 ± 0.35) × 1014 (M·sec)-1 were estimated for the unimolecular decomposition of carbamyl radicals in the high and low pressure limits.

Notes: The reaction of hydrogen atoms with diazomethane was used as a source of methyl radicals to study the reaction of oxygen atoms with methyl radicals. This investigation verifies directly the earlier results that formaldehyde is a major product and that the rate constant is greater than 3×10-11cm3 molecule-1 sec-1.

Notes: The relative intensities of phosphorescence of SO2(3B1) molecules have been determined following the optical excitation of SO2(1B1) molecules by a 2662 Å laser pulse. From a kinetic treatment of these measurements, the intersystem crossing ratio, k2b/(k1b + k2b), was determined; SO2(1B1) + M → SO2(3B1) + M (2b); SO2(1B1) + M → SO2 + M (1b). With M = O2, N2, Ar, CO2, and CO, k2b/(k1b + k2b) = 0.030 ± 0.013, 0.034 ± 0.029, 0.025 ± 0.005, 0.052 ± 0.014, and 0.045 ± 0.028, respectively. These data allow a new, more quantitative evaluation of the extent of involvement of the “excess” triplet SO2 in the 3130 Å-irradiated mixtures of SO2 and CO at high pressures [5, 6]. The new data are also of direct interest in the determination of the theoretical maximum rates of photooxidation of SO2 in the sunlight-irratiated atmosphere of the earth.

Notes: The I2-catalyzed isomerization of allyl chloride to cis- and trans- l-chloro-l-propene was measured in a static system in the temperature range 225-329°C. Propylene was found as a side product, mainly at the lower temperatures. The rate constant for an abstraction of a hydrogen atom from allyl chloride by an iodine atom was found to obey the equation log [k,/M-1 sec-1] = (10.5 ± 0.2) -; (18.3 ± 10.4)/θ, where θ is 2.303RT in kcal/mole. Using this activation energy together with 1 ± 1 kcal/mole for the activation energy for the reaction of HI with alkyl radicals gives DH0 (CH2CHCHCl—H) = 88.6 ± 1.1 kcal/mole, and 7.4 ± 1.5 kcal/mole as the stabilization energy (SE) of the chloroallyl radical. Using the results of Abell and Adolf on allyl fluoride and allyl bromide, we conclude DH0 (CH2CHCHF—H) = 88.6 ± 1.1 and DH0 (CH2CHCHBr—H) = 89.4 ± 1.1 kcal/ mole; the SE of the corresponding radicals are 7.4 ± 2.2 and 7.8 ± 1.5 kcal/mole. The bond dissociation energies of the C—H bonds in the allyl halides are similar to that of propene, while the SE values are about 2 kcal/mole less than in the allyl radical, resulting perhaps more from the stabilization of alkyl radicals by α-halogen atoms than from differences in the unsaturated systems.

Notes: The reactions of singlet molecular oxygen (O21Δg) with a series of organic compounds have been studied in the gas phase at 298°K. The concentration of singlet molecular oxygen was determined by titration with 2,5-dimethylfuran. The titration technique was checked using a photoionization technique. Absolute rate constants were measured on the basis of the loss of organic reactant and, in some cases, of singlet molecular oxygen. It was found that the usual method of producing singlet molecular oxygen in the gas phase can also, under some conditions, allow reactive species other than singlet molecular oxygen to enter the reactor, leading to serious errors in the determination of rate constants. This problem was eliminated by carrying out the rate measurements in the presence of a small amount of nitrogen dioxide a radical scavenger.

Notes: The reaction of iodine with allyl alcohol has been studied in a static system, following the absorption of visible light by iodine, in the temperature range 150-190°C and in the pressure range 10-200 torr. The rate-determining step has been found to be and k3 is consistent with the equation From the activation energy and the assumption E-3 = 1 ± 1 kcal mol-1, it has been calculated that kcal mol-1. The stabilization energy of the hydroxyallyl radical has been found to be 11.4 ± 2.2 kcal mol-1.

Notes: In recent publications from this laboratory, we have shown that the fragmentation of photoexcited olefinic molecules in the vacuum UV region leads mainly to the cleavage of a C - C bond located in the ß position relative to the double bond. The allyl fragment bears away part of the excess energy of the photon. At low pressure, this excited radical is capable of undergoing further decomposition. From the pressure effect, we were able to measure the first order rate constant for this secondary fragmentation. In this paper we shall use RRKM calculations in order to get a better idea on how the energy is distributed among the primary fragments. In cases where α- and β;-methallyl radicals were involved, the results show that an important part of the excess energy is located in the methallyl fragment in the 7.1 and 7.6 eV photolysis of 3-methyl-1-butene, 2-methyl-1-butene, and cis-2-pentene.

Notes: A chain mechanism is proposed to account for the very rapid termination reactions observed between alkyl peroxy radicals containing α-C - H bonds which are from 104 to 106 faster than the termination of tertiary alkyl peroxy radicals. The new mechanism is with termination by. \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R}\overline {{\rm CHOO}} $\end{document} is the zwitterion originally postulated by Criegee to account for the chemistry of O3-olefin addition. Heats of formation are estimated for \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {{\rm CH}_2 {\rm OO,}} {\rm }\overline {{\rm RCHOO}} $\end{document}, and \documentclass{article}\pagestyle{empty}\begin{document}$ ({\rm C}\overline {{\rm H}_3 )_2 {\rm COO}} $\end{document} and it is shown that all steps in the mechanism are exothermic. The second step can account for (1Δ)O2 which has been observed. k1 is estimated to be 109-2/θ liter/M sec where θ = 2.303RT in kcal/mole. The second and third steps constitute a chain termination process where chain length is estimated at from 2 to 10. This mechanism for the first time accounts for minor products such as acid and ROOH found in termination reactions. Trioxide (step 3) is shown to be important below 30°C or in very short time observations (〈10 s at 30°C). Solvent effects are also shown to be compatible with the new mechanism.

Notes: Flash photolysis technique has been used to obtain the rate and thermodynamic parameters of the reversible dimerization reactions of a range of ten phenoxy radicals (I-X) in a toluene-dibutylphthalate mixture (0.6 cP ≤η≤18.4 cP): \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm R}^{.} + {\rm R}^{.} {\mathop{{\buildrel{-\!\!\longrightarrow}\over{\longleftarrow}}}\limits_{k_{-1}}^{k_1}}{\rm D} $$\end{document} The main reason for the difference in the k1 values are the different steric hindrances in radicals. It has been found that the values of k1 for 2,6-diphenyl-4-methoxy- (I), 2-phenyl-(III), and 2-methoxyphenoxy (IV) radicals are 3-5 times smaller than the respective diffusion constants calculated according to the Debye formula with regard to the spin-statistical factor: \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{diff} = \sigma \frac{{8{\rm RT}}}{{3000{\rm \eta }}} $$\end{document} The resultant ΔH1≠values for these radicals in toluene and dibutylphthalate are close to the activation energies of the viscous flow of the solvents B. Linear relationships with a slope equal to unity are observed between log k1 and log(T/η). The recombination of radicals I, III, and IV is limited by translational diffusion. The k1 values for 2,6-diphenyl- (VII), 2,6-di-tert-butyl- (IX), and 2,6-di-tert-butyl-4-methylphenoxy (X) radicals are 10-60 times smaller than kdiff and Δ H≠ B. In the case of radical X in toluene ΔH1≠ 0. The recombination of these three radicals includes an intermediate step of complex formation: \documentclass{article}\pagestyle{empty}\begin{document}$${{\rm R}^\cdot+{\rm R}^\cdot}{\mathop {{\scriptstyle\longleftarrow}^{\hskip-13pt\longrightarrow}}}{\rm R^\cdot}\ldots {\rm R}^\cdot \rightarrow {\rm D}$$ \end{document} For 4-phenyl- (II), 2,6- dimethoxy- (V), 2,4-diphenyl- (VI), and radicals VII, IX, and X the linear relationships between log k1 and log (T/η) have a slope of from 0.5 ± 0.05 to 0.8 ± 0.05. The k1-1 versus η relationships for these radicals are not straight lines. The recombination of these six radicals is limited by translational and rotational diffusion. With the aid of theoretical models, the k1 versus η relationships have been used to derive the steric factor f in radical recombination and the angle θ between the axis and the solid angle generatrix. The solid angle defines the reaction spot on the radical-sphere surface. The recombination of the 2,6-diphenyl-4-diphenylmethylphenoxy radical (VIII) takes place in the region intermediate between the diffusion and the kinetic ones, and the relationship between log k1 and log (T/η) for this radical has a plateau portion. The log k-1 versus log (T/η) relationships have precisely the same form as the corresponding k1 relationships, which is quite in line with the theory of diffusion-controlled reversible recombination reactions.

Notes: A new mechanism for gas phase ozone-olefin reactions is proposed. The mechanism involves biradical intermediates which can react in a variety of ways. One of the possible reaction modes corresponds to the Criegie mechanism originally proposed to explain solution ozonolysis reactions and generally also accepted in the past for gas phase reactions. However, an examination of the gas phase data on ozone-olefin reactions and of the thermochemical and kinetic requirements for these reactions indicates that the Criegie reaction mode may be the least important of various other reaction possibilities. Those other reaction possibilities involve intramolecular H abstractions and rearrangements in biradical intermediates. The proposed mechanism provides very reasonable explanations for a number of unusual observations on gas phase ozonolysis. These are the formation of peroxidic bound products, aldehyde and 1,2-dicarbonyl product fluorescences, and unexpected carbonyl product formations.

Notes: The rate constant for the combination of 2,2-dichloro-1,1,1-trifluoroethyl radicals has been measured by applying the rotating sector technique to the gas phase photochlorination of 2,2-dichloro-1,1,1-trifluoroethane at 315°K. The observed value is 6.89 × 1012 cc/mole.sec. This value is in excellent agreement with measurements by Wampler and Kuntz which yielded a temperature-independent value of 6.6 × 1012 cc/mole.sec. The measurement by Wampler and Kuntz was determined from the photochemical system (CF3CCl3 + C-C6H12 + hν). The Arrhenius parameters for the reaction CF3CCl2· + Cl2 → CF3CCl3 + Cl were found to be given by the expression log k3 = 12.10 - 5830/2.3RT (units in mole, cc, and sec). This is a relatively high activation energy for a chlorination reaction and makes the reaction ever slower than the chlorination of chloroform.

Notes: The methyl and ethyl chlorides and bromides, as well as methyl iodide, were photoionized in the vacuum ultraviolet at 300 K in a mass spectrometer over the pressure range 0.5 to approximately 100 millitorr. Under these conditions, stabilized parent ion dimers are found in CH3Br, CH3I, and C2H5Br, but not in the chlorides. Lower limits for the dissociative lifetimes of the ion-molecule collision complexes were estimated and are as follows: (CH3Br)2+, 1.6 μs; (CH3I)2+, 1.9 μs; and (C2H5Br)2+, 5.4 μs. An increase in photon energy (internal energy content of the reactant ion) decreases the dissociative lifetime of the collision complex in CH3I.

Notes: Previously reported shock tube studies of the dissociation of HBr in the temperature range of 2100-4200°K have been extended to lower temperatures (1450-2300°K) in pure HBr. The course of reaction was followed by monitoring the radiative recombination emission in the visible spectrum from Br atoms. The results imply that, in the lower range of temperatures, the activation energy of dissociation, E in the expression AT-2e-E/RT, can be approximated by the HBr bond energy (88 kcal/mole). It was also found that, in this temperature range, the rate of HBr dissociation is sensitive to the Br2 dissociation rate and the HBr + Br exchange rate. When these rates were adjusted to bring computed reaction profiles into agreement with experimental ones, it was found that the higher-temperature data could also be fitted reasonably well with an HBr dissociation activation energy of 88 kcal/mole, contrary to the conclusions of our previous work, which favored an activation energy of 50 kcal/mole. The “best value” for k1Ar, the rate coefficient for HBr dissociation in the presence of Ar as chaperone, appears to be 1021.78 ± 0.3 T-2 10-88/θ cc/mole sec, where θ = 2.3 RT/1000; that for k1HBr, is 1022.66T-210-88/θ. A detailed review is given of the rate coefficients for the other pertinent reactions in the H2-Br2 system, viz., Br2 dissociation and reactions of HBr with H and Br.

Notes: The impact of surface and oxygen on the oxidative pyrolysis of ethane at temperatures above 590°C was studied using a wall-less reactor. At very low conversions under homogeneous conditions, ethene formation begins at the same temperature regardless of whether oxygen is present or absent. Between 0.00 and 0.13% conversion (592-632°C), the rate with oxygen is actually less than the rate in the absence of oxygen. A reversal occurs at about 633°C above which oxygen has a promoting effect. It is concluded that under homogeneous conditions the initiation step in the oxygen-promoted pyrolysis is the same as in the oxygen-free pyrolysis; therefore, initiation by direct attack of oxygen on ethane does not make an important contribution. The decrease in rate observed upon addition of oxygen implies the formation of the relatively unreactive HO2 · radical. As conversion of the HO2 · radical to the more reactive HO · radical becomes significant, the reaction is highly accelerated. If a stainless steel surface is added, the reaction is inhibited at higher conversions in the presence of oxygen. Again at low conversions, a second reversal occurs, and the stainless steel surface acts as a promoter below 649°C. The rate of surfacecatalyzed ethene formation at 590°C equals the rate of homogeneous ethene formation at 630°C.

Notes: The kinetics of the gas-phase decomposition of bicyclo[4.1.0]heptane has been studied over the temperature range of 708-769 K at pressures between 1 and 17 torr. Isomerization to 1-methylcyclohex-1-ene, methylenecyclohexane, and cycloheptene accounts for 96-98% of the primary reaction products and occurs by first-order, homogeneous, nonradical processes. \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{1 - methylcyclohex - 1 - ene3} /s^{ - 1} = 10^{14.98 \pm 0.50} \exp \left( { - 64600 \pm 1700/1.987T} \right) $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{1 - methylenecyclohexane} /s^{ - 1} = 10^{15.08 \pm 0.43} \exp \left( { - 65900 \pm 1400/1.987T} \right) $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{cyclohexane} /s^{ - 1} = 10^{14.82 \pm 0.28} \exp \left( { - 64900 \pm 1000/1.987T} \right) $$\end{document}

Notes: The relative rate constants for the hydrogen atom abstraction by CCl3CH=CH· radical from CH2Cl2, CHCl3, CH3COCH3, CH3CN, C6H5CH3, C6H5OCH3, CH3CHO, and CH3OH in the liquid phase at 20°C have been measured. It was shown that these reaction rate constants are correlated by the two-parameter Taft equation with ρ* = 0.726 ± 0.096, r* = 1.22 ± 0.16. A relationship between r* and bond dissociation energy D(R—H) has been found for the abstraction reactions of different free radicals.

Notes: Shepp's rotating sector theory for determining radical recombination rate constants, kb, has been modified to take account of radical production by a concurrent thermal reaction. A theoretical sector curve expression has been derived which gives the average radical concentration under intermittent illumination as a function of α, the ratio of first-to second-order radical removal rates, n, the ratio of thermal initiation to photoinitiation, and β, the ratio of the flash time to the half time of second-order radical removal. Analysis of the sector curves generated by the modified theory shows that n has a greater effect on kb than α and that the rotating sector method should be applied only to those photochemical systems in which termination by first-order processes is less than 34% (α = 0.52) and thermal initiation is less than 2% (n = 0.02).

Notes: The very low-pressure (VLPP) technique was used to study the pyrolysis of azoethane (AE), azoisopropane (AIP), and 2,2′-azoisobutane (AIB). The low pressure rate constants were related to the high-pressure Arrhenius parameters by means of the RRKM theory. This procedure in itself does not yield an unambiguous set of parameters. However, thermochemical and kinetic arguments are given which support the following values of log k∞ for the pyrolysis of AE, AIP, and AIB, respectively: 16.4-49.7/θ 16.6-47.9/θ, and 16.4-42.8/θ, where θ = 2.303RT in kcal/mole. The flow dependence of kuni was used to estimate the collisional efficiencies of the azo compounds relative to the wall.

Notes: The hydrogen abstraction from the chlorinated ethanes by chlorine atoms has been investigated in the liquid phase. Rate constants relative to that for hydrogen abstraction from chloroform have been measured between 267° and 333°K using a competition technique. The results are compared with gas-phase data.

Notes: The Hg(63P1) photosensitized decompositions of 3-methyl-1-butene, 2-methyl-2-butene, 3,3-dimethyl-1-butene, and 2,3-dimethyl-1-butene have been used to generate 1-methylallyl, 1,2-dimethylallyl, 1,1-dimethylallyl, and 1,1,2-trimethylallyl radicals in the gas phase at 24 ± 1°C. From a study of the relative yields of the CH3 combination products, the relative reactivities of the reaction centers in each of these unsymmetrically substituted ambident radicals have been determined. The more substituted centers are found to be the less reactive, and this is ascribed primarily to greater steric interaction at these centers during reaction. Measurement of the ratio of trans- to cis-2-pentene formed from the 1-methylallyl radical, combined with published values for this ratio at higher temperatures, enabled the differences in entropy and heat of formation of the trans- and cis-forms of this radical to be calculated as 0.62 ± 0.85 J mol-1 K-1 and - 0.63 ± 0.25 kJ mol-1, respectively, at 298K. Approximate values of the disproportionation/combination ratios for reaction of CH3 with 1,1-dimethylallyl and 1-methylallyl have been estimated and used to compute rate constants for the recombinations of tert-butyl and isopropyl radicals that are in agreement with recently published data.

Notes: Di-tert-butylnitroxide (DTBN) is the simplest of the stable nitroxide radicals and is only consumed at temperatures higher than 90°C or in the presence of very reactive substrates. The pyrolysis of DTBN in solution gives, at least at low conversion, 2-methyl-2-nitrosopropane and di-tert-butylnitroxide-tert-butyl ether. The reaction involves, as the rate-limiting step, the cleavage of the C—N bond. This reaction takes place with an activation energy of 33 kcal/mol. DTBN is stable in the presence of styrene, aldehydes, hydrogen peroxide, α-methyl-N-ethyl nitrone, phenol, and triphenylmethane. On the other hand, it reacts readily with diethylhydroxylamine, ascorbid acid, ethanethiol, and hexanethiol. For the two former compounds the reaction involves a hydrogen transfer as the rate-determining step, and the reaction proceeds, a low conversion, with simple second-order kinetics. The reaction with the thiols is complex and shows a clear inductiontime.

Notes: The kinetics of decomposition of trimethylene sulfide to ethylene and thioformaldehyde was investigated in a single-pulse shock tube using the «relative rate» technique. The extent of reaction was measured in the reflected shock regime from 860° to 1170°K, but experimental difficulties limited the useful data to the temperature range of 980°-1040°K. The first-order rate constant was found to be k = 1013.0 exp (-48,200/RT) sec-1. This result sets an upper limit of 50 kcal/mole for the standard enthalpy of formation of CH2S, with 35 kcal/mole as a more likely value. The isomerization of cyclopropane to propene was used for the reference reaction; in turn, this was checked, in a relative rate experiment, against the pyrolysis of cyclohexene.

Notes: Measurements have been made which provide information concerning the rate of energy transfer between vibrationally excited HF and atomic fluorine. It was found that HF (v = 1) deactivates about seven times slower than was determined in previous experiments. The deactivation rate constant for HF (v = 2) is about six times larger than for HF (v = 1).

Notes: In the study of chemical kinetics, many integrated reaction rate equations have the form In [f(A) + a] = bt + c, where a, b, and c are constants and f(A) is some function of the concentration of a reactant (or product) which can be calculated from the data. The left-hand side of this equation cannot be graphed versus time if the constant a is unknown. However, it is shown that f(A2) varies linearly with f(A1) if A2 is the concentration of reactant measured at a constant time interval later than A1. The constants a and b can be determined from the linear graph. A number of specific examples are considered.

Notes: Detection of atoms by mass spectrometry has been used to study the reactions of hydrogen azide, HN3, with H atoms and active nitrogen, in a fast flow reactor at pressures of about 1 torr. Stoichiometry and products of the H + HN3 reaction have been determined and the rate constant of the initial step, assumed to be H + HN3 → NH2 + N2, was found to be 2.54 × 10-11 exp (-4600/RT) cm3 molecule-1 s-1, in the temperature range of 300-460K. The formation of NH3 and H2 products has been discussed from the different secondary steps which may occur in the mechanism. For the reaction of active nitrogen with HN3, evidence has been found for the participation of excited nitrogen molecules produced by a microwave discharge through molecular nitrogen. The influence of excited nitrogen molecules has been reduced by lowering the gas flow velocity. It was then possible to study the N + HN3 reaction for which the rate constant of the initial step was found to be 4.9 × 10-15 cm3 molecule-1 s-1 at room temperature. Finally, the occurrence of these elementary reactions has been discussed in the mechanism of the decomposition flame of HN3.

Notes: The thermal decomposition of dimethyl sulfoxide at small extent of reaction has been studied at temperatures of 297-350°C and pressures of 10-400 Torr. The major products CH4, C2H4, and SO2 were shown to follow first-order kinetics. The activation energies for production of each was about 48 kcal·mole-1. A chain mechanism has been postulated in the light of the results of isotopic substitution experiments.

Notes: Measurements of the rate coefficient of the reaction (O3P) + NO2 → O2 + NO have been made at 296°K and 240°K, using the technique of NO2* chemiluminescent decay. Values of 9.3 × 10-12 cm3 molec-1 sec-1 at 296°K and 10.5 × 10-12 cm3 molec-1 sec-1 at 240°K were obtained, in excellent agreement with the recent results of Davis, Herron, and Huie [1]. The earlier lower values may have resulted from loss of NO2 on surfaces.

Notes: Oxygen added in amounts of 0.01-0.1% was found to cause the explosion of an acetylene-chlorine mixture at temperatures as low as -78°C. Explosion occurrence and nature depend on the mode of mixing the reactants, the effect of oxygen being associated with concentration limits. The dependence of explosion-inducing oxygen amounts on temperature, pressure, concentrations of reactants, reactor surface type and area, additions of inert gases, and reaction products were investigated. The effect of light on the C2H2 + Cl2 + O2 was studied. The composition of gaseous products resulting from acetylene-chlorine mixture explosion in the presence of minute amounts of oxygen, from a slow reaction inhibited and noninhibited by oxygen, and also from explosion at 400°C in the absence of oxygen, was determined. The results obtained point to the fact that any acetylene-chlorine mixture flash caused by small amounts of oxygen is a branched chain reaction involving activated particles, chain branching presumably being associated with the decomposition of radical CHCl=CHOO* → CH + HCl + CO2.

Notes: It has been shown that experimental errors of the initial conditions of a second-order reaction can cause erroneous results with the rate constant calculated directly from the differential or integrated rate expression. By means of a computer method, a differential technique has been developed so that precise initial reactant conditions are not necessary for calculating a second-order rate constant if continuous measurements of a single reaction variable are available. The technique has been successfully applied to the data of Kistiakowsky and Lacher on the condensation of acrolein and butadiene.

Notes: The effects of reaction barrier height and initial rotational excitation of the reactants on the overall rate of H atom exchange between atomic chlorine and HCl (v = 0) and on the 0 → 1 vibrational excitation of HCl via reactive and nonreactive collisions have been investigated using quasiclassical trajectory techniques. Two empirical LEPS potential energy surfaces were employed in the calculations having reaction barrier heights of 9.84 and 7.05 kcal mol-1. Trajectory studies of planar collisions were carried out on each surface over a range of relative translational energies with the ground-state HCI collision partner given initial rotational excitation corresponding J = 0, 3, and 7. Initial molecular rotation was found to be relatively inefficient in promoting the H atom exchange; the computed rate coefficient for H atom exchange between Cl + HCl (v = 0, J = 7) was only 4 times larger than that for CI + HCI (v = 0, J = 0). The vibrational excitation rate coefficient exhibited a stronger dependence on initial molecular rotational excitation. The observed increase in the vibrational excitation rate coefficient with increasing initial molecular rotational excitation was due primarily to nonreactive intermolecular R → V energy transfer. The vibrational excitation rate coefficients increase with decreasing reaction barrier height.

Notes: Disagreements in rate constants and parameters between published results on the decomposition of 1,1-difluoroethane and 1,1,1-trifluoroethane are shown to originate from incorrect specification and setting of reaction conditions in one of the studies. When corrected, applicable results are in excellent agreement.

Notes: The rate of the reverse reaction of the system has been measured in the range of 584-604 K from a study of the azomethane sensitized pyrolysis of isobutane. Assuming the published value for the rate constant of recombination of t-butyl we obtain \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k_{{\rm - 1}} (\sec ^{- 1}) = 14.67 - 39.4\,{\rm kcal}/{\rm mol}/(2.3{\rm RT}) $$\end{document} Combination with our published data for k1 permits the evaluation \documentclass{article}\pagestyle{empty}\begin{document}$$ \log K_1 ({\rm atm}^{ - 1}) = 7.94\,\,{\rm at}\,\,600{\rm K} $$\end{document}We have modified a previously published structural model of t-butyl by the inclusion of a barrier to free rotation of the methyl groups in order to calculate values of the entropy and enthalpy of t-butyl as a function of temperature. Using standard data for H and for i-C4H8 we obtain \documentclass{article}\pagestyle{empty}\begin{document}$$ \Delta H_ f^\circ(t - {\rm butyl},\,300\,{\rm K})({\rm kcal}/{\rm mol}) = 10.6 \pm 0.5 $$\end{document}We have obtained other, independent values of this quantity by a reworking of published data using our new calculations of the entropy and enthalpy of t-butyl. There is substantial agreement between the different values with one exception, namely, that derived from published data on the equilibrium \documentclass{article}\pagestyle{empty}\begin{document}$$ i - {\rm C}_{\rm 4} {\rm H}_{{\rm 10}} + {\rm I}\rightleftharpoons t{-} {\rm C}_4 {\rm H}_9 + {\rm HI} $$\end{document} which is significantly lower than the other values.We conclude that the value \documentclass{article}\pagestyle{empty}\begin{document}$$ \Delta H_ f^\circ(t - {\rm butyl},\,300\,{\rm K})({\rm kcal}/{\rm mol}) = 10.5 \pm 1.0 $$\end{document}obtained from the present work and a reworking of published data which involves the use of experimental data on t-butyl recombination is incompatible with the result based on iodination data.

Notes: The kinetics of the reaction have been investigated in H2SO4 medium under different conditions. The observed bimolecular rate constant kobs, has been found to depend on [H+]-0.55 and to increase with the initial concentration ratio of the reactants R0 = [H2O2]0/[U (IV)]0 above 0.49. The activation energy of the overall reaction has been determined as 13.79 and 14.3 kcal/mol at R0 = 1 and 0.35, respectively. Consistent with experimental data, a detailed reaction mechanism has been proposed where the hydrolytic reaction (4) followed by the rate-controlling reaction (10) and subsequent fast reactions of U (V) and OH radicals are involved: A kinetic expression has been derived from which a graphical evaluation of (kK4)-1 and k-1 has been made at R0 = 1 as (12.30 ± 0.09) × 10-3 M min, (6.23 ± 2.19) × 10-4 M min; and at R0 = 0.35 as (12.63 ± 2.13) × 10-3 M min, (8.32 ± 6.62) × 10-4 M min, respectively. Indications of some participation of a chain reactionat R0 = 1 have been obtained without affecting thesecond-order kinetics as observed.

Notes: The kinetics of thermal decomposition of ethyl, isopropyl, and t-butyl trifluoroacetates have been studied in the gas phase. In each case initial decomposition follows the normal ester route to give an olefin and trifluoroacetic acid, and elimination of hydrogen fluoride does not occur. However, trifluoroacetic acid is thermally unstable at ethyl and isopropyl ester decomposition temperatures, and further products result, including those from the difluorocarbene produced by decomposing trifluoroacetic acid. Placing a CF3 group at an ester's γ carbon increases the polarity of its transition state and decreases its thermal stability. The activation energies of the ethyl and isopropyl esters are lowered by 3.8 and 4.7 kcal/mol compared to the corresponding acetates, and the primary decomposition kinetics, which are homogeneous and of the first order, are expressed by α-Methylation enhances the reactivity of the trifluoroacetates, and the t-butyl ester, the transition state for which is sufficiently polar for heterogeneous decomposition to occur, shows signs of thermal instability at room temperature. The equilibrium was also investigated and gave ΔH° = +13,580 cal/mol and ΔS° = +31.07 gibbs/mol in the forward direction. The results obtained extend and support the known structure-rate correlations in the gas-phase elimination of esters.

Notes: The thermal unimolecular decomposition of ethylbenzene, isopropylbenzene, and tert-butylbenzene was studied using the very-low-pressure pyrolysis (VLPP) technique. Each reactant decomposed by way of β C—C bond homolysis, producing methyl radicals and benzyl or benzylic-type radicals. RRKM calculations show that the observed rate constants, when combined with thermochemical estimates, are consistent with the following high-pressure rate expressions: \documentclass{article}\pagestyle{empty}\begin{document}$ \log k(\sec ^{ - 1}) = 15.3 - (72.7/{\rm \theta)} $\end{document} for ethylbenzene between 1053 and 1234 K, \documentclass{article}\pagestyle{empty}\begin{document}$ \log k(\sec ^{ - 1}) = 15.8 - (71.3/{\rm \theta)} $\end{document} for isopropylbenzene between 971 and 1151 K, and \documentclass{article}\pagestyle{empty}\begin{document}$ \log k(\sec ^{ - 1}) = 15.9 - (69.1/{\rm \theta)} $\end{document} for tert-butylbenzene between 929 and 1157 K, where θ (kcal/mol) = 2.303RT. Resulting activation energies combined with heat capacity and heat of formation data led to the following dissociation enthalpies and enthalpies of formation at 298 K: DH° (øCH(CH3)—CH3) = 73.8 kcal/mol, ΔHf° (øÇCH(CH3)) = 39.6 kcal/mol, DH° (øC(CH3)2—CH3) = 72.9 kcal/mol, and ΔHf° (øÇ(CH3)2) = 32.4 kcal/mol. Derived high-pressure rate constants are in good accord with results of lower temperature toluene- and aniline-carrier experiments.

Notes: Chloroethanes react with aqueous caustic to yield either elimination or substitution products. The reaction rates were measured for the dichloroethanes, trichloroethanes, tetrachloroethanes, and pentachloroethane between 283 and 353°K. The constants of HCl eleminations referring to the rate equation \documentclass{article}\pagestyle{empty}\begin{document}$$r = k[{\rm OH}^{\rm - }][{\rm dissolved \,substrate]}$$\end{document} are given by \documentclass{article}\pagestyle{empty}\begin{document}$${\rm 1,2 - C}_{\rm 2} {\rm H}_{\rm 4} {\rm Cl}_{\rm 2} {\rm }\,k = 10^{10.99 \pm 0.03} \exp (- 23,000 \pm 50RT)$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$${\rm 1,1,2 - C}_{\rm 2} {\rm H}_{\rm 3} {\rm Cl}_{\rm 3} {\rm}\,k = 10^{13.99 \pm 0.03} \exp (- 22,400 \pm 50/RT)$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$${\rm 1,1,1,2 - C}_{\rm 2} {\rm H}_{\rm 2} {\rm Cl}_{\rm 4} {\rm }\,k = 10^{15.45 \pm 0.14} \exp (- 25,800 \pm 210/RT)$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$${\rm 1,1,2,2 - C}_{\rm 2} {\rm H}_{\rm 2} {\rm Cl}_{\rm 4} {\rm }\,k = 10^{16.40 \pm 0.05} \exp (- 22,550 \pm 70/RT)$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$${\rm C}_{\rm 2} {\rm HCl}_{\rm 5} {\rm }\,k = 10^{12.50 \pm 0.08} \exp (- 15,200 \pm 110/RT)$$\end{document} all rate constants being in 1./mole·s and R in cal/mole· deg.With ethyl chloride, 1,1-dichloroethane, and 1,1,l-trichloroethane, the elimination is not observed and a slow substitution takes place. The influence of chlorine substituents on both sides of the molecule on mechanism and rate parameters is discussed.

Notes: The occurrence of anchimeric assistance in the vapor-phase thermolysis of anti- and syn-7-acetoxy-7-methylnorbornene and 7-acetoxy-7-methylnorborane has been investigated. The relative rates of thermolysis were found to be 1.9, 0.87, and 1.0, respectively. The nature of the transition state for ester thermolysis is discussed in light of the small amount of anchimeric assistance found in the thermolysis of the anti-isomer.

Notes: The acid-catalyzed enolization of acetone in the presence of bromine is found to be catalyzed by the anionic micelles of sodium dodecyl sulfate. The rate acceleration expected on the basis of lowering of activation energy is largely nullified by the decrease in the entropy of activation, leading to a very small rate enhancement, i.e., kψ/k0 = 1.2 at 30°C. The binding constant for the micelle-substrate complex is determined. The micellar rate enhancement is the same, irrespective of the halogen used, chlorine, bromine, or iodine.

Notes: A study of the thermal decomposition of an acetylene-ethane-d6 mixture indicates that the rate constant for hydrogen abstraction from acetylene by methyl is more than 20 times less than for abstraction from ethane. Isotopic exchange is initiated by a rapid reaction between product D atoms and C2H2. A series of experiments involving the reactions of a D2-acetylene mixture indicated that a molecular exchange process was also occurring, and it was shown that d[C2HD]/dt = k[D2]0.7[C2H2]0.3, effective activation energy = 15.8 kcal/mol. This mechanism made an insignificant contribution to isotope exchange in C2H2-C2D6 mixtures.

Notes: Methyl nitrate decomposition is accompanied by self-heating. Using very fine thermocouples, direct measurements of excess temperatures have been made to establish the intensity and extent of self-heating in nonisothermal reaction. The measurements are displayed as contourlines of equal degrees of temperature excess on the pressure-temperature ignition diagram.A twofold kinetic investigation has been made of the overall reaction. One part concentrates on achieving isothermal conditions and full characterization of intermediate products. It uses mass-spectrometric analyses both to establish stoichiometry throughout decomposition and to validate velocity constant measurements derived from continuous pressure-time records. The best value for E = 151 ± 3 kJ/mol is about 10 kJ/mol less than previously.The other part deliberately invades the nonisothermal region to test the qualitative and quantitative predictions of theory (1) that uncorrected reaction orders and activation energies will exceed their isothermal values, (2) that their relative excess (δn/n, δE/E) will be about the same, and (3) that they will be dependent in a simple and predictable way on the reduced excess central temperature.

Notes: With a continuous jet-stirred tank reactor operating at small space time (0.05-1.2 s) the kinetics of the formation of six minor products (ethane, isobutane, butene-1, 2,3-dimethyl-butane, 4-methylpentene-1, and 1,5-hexadiene) are studied during the pyrolysis of propane, at small extents of reaction and over the temperature range of 600-780°C. The experimental results are in agreement with the free radical mechanism proposed by Jezequel, Baronnet, and Niclause for this reaction. They show that the two most important termination processes are The measured rates of formation of the minor products are consistent with the quasi-identical values estimated by Jezequel and co-workers (between 475 and 505°C) and by Allara and Edelson (between 510 and 560°C) for kinetic parameters (A1 ≃ 1016.65 s-1 and E1 ≃ 84.7 kcal/mole) of the chain initiation process

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: A new mechanism is proposed for gas-phase O3-aldehyde reactions. Certain aspects of the new mechanism may be applicable also to O3-aldehyde reactions in solution. The proposed mechanism involves initiation by addition of O3 across the aldehydic C=O bond. The initiation process and the subsequent chemistry together represent an exact analogue of the Criegee mechanism for O3-alkene reactions.

Notes: The gas-phase kinetics and energetics of the Criegee intermediate, deduced from studies of O3-alkene systems, suggest that a hydroxy-substituted Criegee intermediate probably participates in the photooxidation of formaldehyde. In contradistinction, the existing evidence suggests that the Criegee intermediate and its isomers are probably not involved in alkyldioxy disproportionation reactions. In the case of O + oxoalkane addition reactions, the Criegee intermediate and its isomers are discussed in terms of a complex equilibrium: .

Notes: The kinetics of the thermal reactions of bicyclo[4.2.2]deca-3,7-diene (BDD) and endo- and exo-5-vinylbicyclo[2.2.2]oct-2-ene (endo- and exo-VBO) have been studied in the gas phase. The temperature range was 459-526 K for BDD, 476-563 K for endo-VBO, and 513-578 K for exo-VBO. The initial pressures were varied from 2 to about 40 torr. These compounds isomerize to cis-1,2,4a,5,8,8a-hexahydronaphtalene (HHN) and into each other, and decompose to 1,3-butadiene (BD) + cyclohexa-1,3-diene (CHD). The reactions are homogeneous and first order. Their rate constants (in s-1) are given by: where the superscripts represent the reagents and the subscripts the products. The heats of formation and the entropies of endo-VBO, exo-VBO, and BDD are estimated.

Notes: The rate of adsorption of SO2 on a prototype carbonaceous surface was measured at low pressure in a flow reactor. The measured rate indicates a maximum atmospheric loss of SO2 by heterogeneous reaction of 1%/h for a particle density of 100 μg/m3. The capacity of carbon particles to adsorb SO2 is limited at ∼1 mg SO2 g-1 C. NO2 has no effect on the rate of SO2 adsorption or the saturation behavior.

Notes: The thermal reactions of 1,3-butadiene (BD) with cyclohexa-1,3-diene (CHD) have been studied in a static system between 437 and 526 K. The pressures of BD and CHD were varied from 61 to 397 torr and from 50 to 93 torr, respectively. The percentages of consumed BD and CHD were always kept lower than 14%. The reactions - in the order of importance - are All the reactions are homogeneous and of the first order with respect to the reagents. Their rate constants (in L/mol·s) are given by \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} \log _{10} k_{{\rm HHN}} = - (25,370 \pm 70)/4.576T + (7.02 \pm 0.03) \\ \log _{10} k_{{\rm KNDO}} = - (24,840 \pm 50)/4.576T + (6.58 \pm 0.02) \\ \log _{10} k_{{\rm BDD}} = - (25,530 \pm 50)/4.576T + (6.61 \pm 0.02) \\ \log _{10} k_{{\rm EXO}} = - (26,760 \pm 50)/4.576T + (7.06 \pm 0.02) \\ \end{array} $$\end{document} A thermochemical analysis of a biradical mechanism is in agreement with these results.

Notes: The shock-initiated decomposition of tetramethylgermane (1078-1242 K) has been found to involve successive elimination of methyl radicals with the rate constant k1 for the first step given by \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k_{\rm 1} {\rm}(s^{- 1}) = {\rm}(17.00 \pm 0.35) - (77.0 \pm 1.9)\theta {\rm kcal/mol} $$\end{document} In the presence of excess toluene the products were CH4 (major), C2H4, and C2H6. Results relevant to the reaction of methyl radicals with toluene compared to methyl radical recombination are discussed.

Notes: The gas-phase kinetics of thermal decomposition of ethyl difluoroacetate, pentafluoropropionate, and hepatfluorobutyrate have been studied. The normal ester decomposition route to ethylene plus carboxylic acid is taken in each case, but the fluorinated acids decompose rapidly at the temperatures used. The primary decompositions are homogeneous and unimolecular, and the three Arrhenius equations are \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} \log k{\rm}({\rm CF}_2 {\rm HCO}_2 {\rm Et}){\rm}({\rm s}^{- 1}) = (12.81 \pm 0.39) - (46,740 \pm 1290){\rm cal/mol/2}{\rm .303}RT \\ \log k{\rm}({\rm C}_2 {\rm F}_5 {\rm CO}_{\rm 2} {\rm Et}){\rm}({\rm s}^{- 1}) = (12.16 \pm 0.32) - (43,760 \pm 970){\rm cal/mol/2}{\rm .303}RT \\ \log k{\rm}({\rm C}_3 {\rm F}_7 {\rm CO}_{\rm 2} {\rm Et}){\rm}({\rm s}^{- 1}) = (12.29 \pm 0.13) - (43,880 \pm 370){\rm cal/mol/2}{\rm .303}RT \\ \end{array} $$\end{document} The postulate of a slightly electron-rich γ carbon in six-center ester transition states is supported by the higher rates and lowered activation energies observed when increasingly electron-withdrawing fluorinated groups are linked to this center. The stabilization is reflected in a ρ constant of +0.30. The results are compared with previous work on α substitution in fluorinated esters.