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Notes: The rates and products of the reactions of ozone with acetylene, methylacetylene, dimethylacetylene, and ethylacetylene have been studied in a long-path infrared cell at 21 ± 1°C. The gas phase reaction gives products formed by cleavage of the carbon-carbon triple bond. A mechanism is proposed that involves formation of a short-lived acid anhydride intermediate, which is energized by virtue of the reaction exothermicity and undergoes unimolecular decomposition. Formation of an α-dicarbonyl was observed in every case, but there is evidence that a side reaction on the walls accounted for that product. The general relationship between alkyne and alkene ozonation is discussed. The rate measurements showed that, unlike the alkenes, the rate of alkyne ozonation is not greatly affected by substitution with simple alkyl groups. The rate constant for C2H2 agrees with earlier work and thus provides additional support for the previously derived high A-factor for acetylene ozonation relative to alkenes.

Notes: The pyrolysis of neopentane, at small extents of reaction, was studied by gas chromatography, in Pyrex reaction vessels between 450° and 530°C and in the initial pressure range 25-200 mm Hg. At initial time, this thermal decomposition can be essentially represented by a homogeneous long-chain radical mechanism. The rate constant of the unimolecular initiation process is approximately given by the expression \documentclass{article}\pagestyle{empty}\begin{document}$$k_{\rm 0} \simeq 10^{13} {\rm exp}\left({\frac{{50,000}}{{RT}}} \right){\rm mole}^{- {\rm 1/2}} {\rm .ml}^{- {\rm 1/2}} {\rm .s}^{- {\rm 1}}$$\end{document} The initial rate constant of the global reaction (order 3/2) is nearly equal to \documentclass{article}\pagestyle{empty}\begin{document}$$k_{\rm 1} + 10^{16.8} {\rm exp}\left({\frac{{82,000}}{{RT}}} \right){\rm s}^{- {\rm 1}}$$\end{document} This reaction is strongly inhibited by propene or isobutene and self-inhibited by the isobutene formed; an interpretation of all these inhibition phenomena of the neopentane pyrolysis is proposed. Our observations and conclusions, which have been summarized in communications during 1968 and 1969, are compared to those of other authors, particularly to the recent ones of Purnell and colleagues [13] and of Taylor and colleagues [14], [15].

Notes: Methods of linear algebra are applied to (a) the problem of determining whether detailed balancing for some or all stages of a chemical process is implicit from the existence of steady state for some or all of the chemical species involved, and (b) the formulation of general concentration-type equilibrium relationships solely from kinetic considerations and the assumption of full detailed balancing.

Notes: Ozone was photolyzed at room temperature in the presence of N2O at 2537 Å and 2288 Å to produce O(1D) atoms. These atoms can react with either O3 or N2O via From the quantum yield of N2, the relative rate constants k6a/k6 and k2/k6 could be obtained, where k6 + k6a + k6b. The former rate constant ratio was found to be 0.37 ± 0.03 at 2537 Å and 0.33 ± 0.03 at 2288 Å, in good agreement with an earlier report from our laboratory. The ratio k2/k6 was found to be 2.6 at 2537 Å, but 4.1 at 2288 Å. The difference in the two numbers, if real, may reflect differences in reactivity due to different amounts of excess translational energy in the O(1D) atom at the two wavelengths.

Notes: Disproportionation-combination ratios have been obtained for small alkyl radicals produced in the mercury-photosensitized hydrogenation of ethylene, propylene, butene-1, butene-2, and isobutene. For conditions favoring thermalized radicals, kd/kc (ethyl, ethyl) = 0.14, kd/kc (isopropyl, isopropyl) = 0.69, kd/kc (isopropyl, n-propyl) = 0.41, kd/kc (2-butyl, 2-butyl) = 0.77, kd/kc (2-butyl, n-butyl) = 0.45, and kd/kc (t-butyl, t-butyl) = 3.1. The results are consistent with kd/kc (n-propyl, n-propyl) = 0.15 and kd/kc (n-butyl, n-butyl) = 0.14. The general agreement between these disproportionation-combination ratios and those obtained where photolytic radical sources have been used indicates that under appropriate conditions, H atom addition to olefins is a suitable source for the study of thermalized alkyl radicals and may be especially useful for larger alkyl radicals for which clean photolytic precursors are not available.

Notes: The disproportionation-combination reactions of radicals 4,4-dimethylpentyl-2 and 2,4-dimethylpentyl-2, produced by collisional stabilization of the respective chemically activated species, have been studied at 298°K, with and without getter radicals. Use of getters t-C4H9 and C2H5 with 4,4-dimethylpentyl-2, and of iso-C3H7 with 2,4-dimethylpentyl-2 yielded disproportionation-combination ratios ω for parent-getter and t-C4H9-C2H5 cross reactions, and for the mutual reaction of t-C4H9 radicals. The unstabilized hot radicals decompose, and these experiments also yielded values for the high-pressure rate constant ka∞ of 1.70 × 108sec-1 and 2.11 × 107sec-1 for 4,4-dimethylpentyl-2 and 2,4-dimethylpentyl-2, respectively. The results, compared to those for other large alkyl radical systems obtained earlier, suggest that steric effects influence the accessibility of H atoms for transfer.

Notes: The gas phase reactions of PhCOOCH3 with I2 and Br2 were studied spectrophotometrically in a static system over the temperature ranges 344-359° and 246-303°, respectively. For each system the initial rate was first order in PhCOOCH3 and half order in halogen as the concentration of PhCOOCH3 was varied from 1.4 to 15.2 torr, that of I2 from 6.2 to 26.4 torr, and that of Br2 from 3.0 to 13.6 torr. The rate-determining step is the extraction of a methoxyl hydrogen atom: Empirical assignment of A-factors for k1 lead to \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log(k}_{\rm 1} {\rm /M}^{- {\rm 1}} {\rm sec}^{- {\rm 1}} {\rm) = (11}{\rm .5} \pm {\rm 0}{\rm .3)} - (29.9 \pm 0.8)/\theta $$\end{document} for the I2 system, and to \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log(k}_{\rm 1} {\rm /M}^{- {\rm 1}} {\rm sec}^{- {\rm 1}} {\rm)} = {\rm (11}{\rm .3} \pm {\rm 0}{\rm .3)} - (14.6 \pm 0.8)/\theta $$\end{document}for the Br2 system, where φ = 2.303RT in kcal/mole. Combined with the assumption that E-1 = 1 ± 1 kcal/mole and 2 ± 1 kcal/mole for HI and HBr, respectively, DH2980 (PhCOOCH2—H) calculated from the two systems shows excellent agreement at 100.2 ± 1.3 kcal/mole and 100.1 ± 1.3 kcal/mole. Using a value of δHf,2980 (PhCOOMe) = -65.6 ± 1.5 kcal/mole obtained from group additivity estimates, δHf,2980 (PhCOOCH2) is calculated to be -16.7 ± 2.0 kcal/mole. Unimolecular decomposition of the Ph(CO)O°CH2 radical was also observed: \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm Ph}\left( {{\rm CO}} \right){\rm O\dot CH}_{\rm 2} \mathop {\hbox to 20pt{\rightarrowfill}}\limits^3 {\rm Ph\dot CO} + {\rm H}_{\rm 2} {\rm CO} $$\end{document} with a rate constant equal to \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log(}k_{\rm 3} {\rm /sec}^{- {\rm 1}} {\rm)} = {\rm (15} \pm {\rm 0}{\rm .5)} - (26 \pm 3)/\theta $$\end{document} The abnormally high methoxyl C—H bond strength is discussed in relation to the bonding in ethers, alkanes, and esters.

Notes: A critical evaluation of the rates of the dissociation and recombination reactions of fluorine and chlorine is given. Data are presented graphically and in tabular form. The effect of various third bodies is discussed. Rate expressions for specified temperature ranges are recommended, while comparison with theoretical values obtained from the Benson and Fueno theory is made where applicable.

Notes: The photolysis of 1,1,3,3-tetrafluoroacetone has been reinvestigated as a source of CHF2 radicals at temperatures up to 578°K, and the following rate constant ratio was determined for the reactions θ= 2.303 RT in kcal/mole. 1,1-Difluoro- and 1,1,3,3-tetrafluoroacetone were photolyzed in the presence of tetramethylsilane, and Arrhenius parameters were measured for the hydrogen abstraction reactions: R + Me4Si → RH + Me3SiCH2 TextRT(°K)E (kcal/mole)log A (mole-1cc sec-1)log k (500°K) (mole-1cc sec-1)CH2F473-58612.00 ± 0.3011.68 ± 0.126.44CHF2416-52610.18 ± 0.3311.65 ± 0.157.21By comparing with previous data on the CH3 and CF3 reactions, the activation energies were interpreted in terms of the enthalpy changes for the reactions and a polar effect operative between the attacking fluoromethyl radicals and the substrate which tends to reduce the activation energy progressively as the fluorine content of the radical increases. This polar effect, which decreases the activation energy for hydrogen abstraction from SiMe4 along the series CH3, CH2F, CHF2, and CF3, is in marked contrast to the polar repulsion between the fluorinated radicals and SiHCl3 which was tentatively proposed to explain the increase in activation energy observed in the same series of reactions with SiHCl3.

Notes: Long-chain chlorine-photosensitized oxidation has been observed in the gas phase at about 355°K for 1,1,2,2- and 1,1,1,2-C2H2Cl4, C2HCl5, and C2Cl4 but not for C2H6, 1,2-C2H4Cl2, 1,1,1-C2H3Cl3, C2H4, and 1,2-C2H2Cl2. This is shown to depend on the exothermicity of the dissociation of the chloroethoxy radicals which must be involved in each reaction system.

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: The photolysis of pure N2O, N2O and N2, and N2O and C3H6 mixtures at 1470 Å and room temperature has been studied to determine the relative importance of the primary processes. The results are where φ{O(1D)} = 0.515 represents both the O(1D) produced in the primary act and that produced by collisional quenching of O(1S); φ{N2(3Σ)} = 0.084 represents only that portion of N2(3φ) which dissociates N2O on deactivation; and φ{O(1S)} = 0.38 - ±{N(2D)} represents only that portion of O(1S) which enters into chemical reaction with N2O. If the reaction of O(1S) with N2O yields only N2 and O2 as products, which seems likely from potential-energy curve considerations then ±{O(1S)} = 0.135 ± 0.06 and φ{N(2D)} = 0.245 ± 0.06. Young and coworkers [4] have found from spectroscopic observations that the total quantum yield of O(1S) is about 0.5. Thus it can be concluded that collisional removal of O(1S) by N2O yields mainly O(1D) with chemical reaction being less important. Furthermore, most of the O(1D) is produced this way, and the true primary yield of O(1D) is about 0.15. The metastable N(2D) is not deactivated by N2O, but is removed by chemical reaction to produce N2 and NO. The results further indicate that N2(3Σ) dissociates N2O at least 80% of the time during quenching. The relative efficiency of N2O compared to N2 is about 2 for the removal of O(1D). O(1S) is removed about 90 times as efficiently by C3H6 as by N2O.

Notes: The gas phase photolysis of CCl4 in the presence of several alkanes has been used to obtain Arrhenius parameters for the abstraction of hydrogen atoms by the CCl3 radical: The following log k4 values were obtained: TextRHlog k4c-C5H10,\documentclass{article}\pagestyle{empty}\begin{document}$$12.00 \pm 0.21 - \frac{{10,700 \pm 400}}{{2.3RT}}$$\end{document}n-C6H14\documentclass{article}\pagestyle{empty}\begin{document}$$11.81 \pm 0.18 - \frac{{10,800 \pm 300}}{{2.3RT}}$$\end{document}2,3-Dimethylbutane\documentclass{article}\pagestyle{empty}\begin{document}$$10.88 \pm 0.11 - \frac{{8,200 \pm 200}}{{2.3RT}}$$\end{document}c-C7H14\documentclass{article}\pagestyle{empty}\begin{document}$$12.07 \pm 0.43 - \frac{{9,900 \pm 800}}{{2.3RT}}$$\end{document}Methylcyclohexane\documentclass{article}\pagestyle{empty}\begin{document}$$11.75 \pm 0.26 - \frac{{9,900 \pm 500}}{{2.3RT}}$$\end{document}c-C8H16\documentclass{article}\pagestyle{empty}\begin{document}$$12.11 \pm 0.29 - \frac{{9,600 \pm 500}}{{2.3RT}}$$\end{document}The results are compared to those for CH3 and CF3 radicals.

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 rate of the gas phase reaction \documentclass{article}\pagestyle{empty}\begin{document}$$\Delta - {\rm CH}_{\rm 2} - {\rm I + I} \cdot {\rightleftharpoons}\Delta - {\rm CH}_{\rm 2} \cdot + {\rm I}_{\rm 2}$$\end{document} has been measured spectrophotometrically over the range 480°-550°K. The rate constant fits the equation \documentclass{article}\pagestyle{empty}\begin{document}$${\rm log}k{\rm (M}^{- {\rm 1}} {\rm sec}^{- {\rm 1}} {\rm)} = {\rm (11}{\rm .4} \pm {\rm 0}{\rm .1)} - (16.8 \pm 0.2)/\theta$$\end{document} where θ = 2.303RT in kcal/mole. This result, together with the assumption that the activation energy for the back reaction is 0 ± 1 kcal/mole, allows calculation of DH0298 (Δ—CH2—H) = 97.4 ± 1.6 kcal/mole and ΔH0f 298 (Δ—CH2·) = 51.1 ± 1.6 kcal/mole. These values correspond to a stabilization energy of 0.4 ± 1.6 kcal/mole in the cyclopropylcarbinyl radical.

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 decomposition rate constant of i-PrI under conditions of very low-pressure pyrolysis (VLPP) is completely consistent with the well-known high-pressure Arrhenius parameters and the RRK(M) theory. The decomposition of n-PrI under the same conditions proceeds via two pathways, the anti-Markownikoff dehydroiodination and C—I bond scission. The data, analyzed by taking into account the mutual interaction of the two pathways, is completely consistent with the known Arrhenius parameters for the bond scission step and, when combined with a reasonable A-factor, yields an activation energy for HI elimination which is as predicted for these semi-ion pair transition states.

Notes: The kinetics of the thermal elimination of HF from 1,2-difluoroethane \documentclass{article}\pagestyle{empty}\begin{document}$${\rm CH}_{\rm 2} {\rm FCH}_2 {\rm F} \to {\rm CH}_{\rm 2} = {\rm CHF} + {\rm HF}$$\end{document} have been studied in a static system over the temperature range 734-820°K. The reaction was shown to be first order and homogeneous, with a rate constant of \documentclass{article}\pagestyle{empty}\begin{document}$${\rm log }k_2 ({\rm s}^{- {\rm 1}} {\rm)} = {\rm 13}{\rm .39} \pm {\rm 0}{\rm .2} - (62.9 \pm 0.9)/\theta$$\end{document} where θ = 2.303RT in kcal/mole. The A-factor falls within the normal range for such reactions and is in line with transition state theory; the activation energy is similarly consistent with an estimate based on data for the analogous reactions of ethyl fluoride and other alkyl halides. The above activation energy has been compared with values of the critical energy calculated from data on the decomposition of chemically activated 1,2-difluoroethane by the RRKM theory and the bond dissociation energy, D(CH2F—CH2F) = 88 ± 2 kcal/mole, derived. It follows from thermochemistry that ΔHf0(CH2F) = -7.8 and D(CH2F—H) = 101 ± 2 kcal/mole. Bond dissociation energies in fluoromethanes and fluoroethanes are discussed.

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: During methane oxidation initiated by nitric acid or nitrogen dioxide, it is possible to observe, under certain conditions of temperature, initiator content, and flow rates, the formation of an adiabatic “temperature peak.” Because the maximum temperature of the peak does not exceed the initial temperature of the reactor by more than 220°C, the recorded temperature-increase curves were used for a kinetic interpretation. The obtained kinetic parameters (overall n and E) agree with the values reported in the literature for isothermal methane oxidation and suggest that the overall mechanism does not change in the conditions of “temperature peak.”

Notes: A study of the structural isomerization rate of chemically activated 1,1-dimethylcyclopropane from singlet methylene addition to the double bond of isobutene is reported. Singlet methylenes were produced from the 4358- and 3660-Å photolysis of diazomethane in the presence of added oxygen. Theoretical rates calculated via RRKM theory are in excellent agreement with experiment for calculations utilizing activated complex structures and critical energies consistent with known thermal Arrhenius parameters, and excitation energies consistent with previous determinations of ΔHf00(CH2) + E*(CH2) = 116.1 and 112.6 kcal/mole for diazomethane photolyses at 3660 and 4358 Å, respectively.

Notes: The photolyses of 1,3-difluoro- and 1,1,3,3-tetrafluoroacetone have been reinvestigated as sources of fluoromethyl radicals, and the following rate constant ratios were determined θ= 2.303 RT in kcal/mole. The results are in substantial agreement with the original investigations. The photolyses of the fluoroacetones were used as sources of CH2F and CHF2 radicals, and the following Arrhenius parameters were obtained for the hydrogen abstraction reactions R + SiHCl3 → RH + SiCl3: TextRT(°K)E (kcal/mole)log A (mole-1 cc sec-1)log k (400°K) (mole-1 cc sec-1)CH2F335-4436.06 ± 0.1510.79 ± 0.087.48 CHF2CHF2334-4426.82 ± 0.0911.32 ± 0.057.59The rates of reactions of CH2F and CHF2 radicals toward hydrogen abstraction from SiHCl3 are an order of magnitude lower than the corresponding rates for the CH3, C2H5, and CF3 radicals as a result of increased activation energies for the CH2F and CHF2 reactions. The interpretation of the results is hindered by a lack of accurate thermochemical data on the radicals. The activation energies, as they stand, can be rationalized in terms of a polar repulsion between SiHCl3 and the radicals, increasing regularly and leading to a progressive increase in activation energy with increasing fluorine substitution in the radical. This interpretation is consistent with the estimates D(CH2F—H) ∝ D(CHF2—H) ∝ 97 kcal/mole. On the other hand, there is some indication, from the spread of A-factors in the series of fluoromethyl radicals reacting with SiHCl3, that internal compensation of Arrhenius parameters is occurring in some of the reactions; and when this is taken into account, the interpretation of activation energies is more difficult.

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 Pyrolysis of ethyl formate has been carried out in the temperature range 557°-630° and the rate expression k = 1012.34 e-48,100±500/RT sec-1 was obtained, in agreement with the prediction of O'Neal and Benson [1]. Calculated Arrhenius A-factors and experimental rate constants have been used to obtain the activation energies for the decomposition of the following compounds by the six-center molecular mechanism (in kcal/mole): 2-pentanone 59; methoxyacetone, 58; 2,4-pentanedione, 51; methyl butyrate, ≥ 70; 1-heptene, 54, and 4-methyl-1-hexene, 54-55.

Notes: By monitoring the relative concentrations of mercury 3P0 atoms using absorption photometry, absolute rate constants have been measured for the excimer-forming reaction Hg (3P0) + Hg + N2 → Hg2* + N2 and for the quenching of Hg (3P0) atoms by ethane, propane, deuterated propanes, and nitrous oxide.

Notes: In dissociation experiments of H2O2 under shock wave conditions, the spectra of H2O2 and HO2 have been observed in the UV at 2200 ≤ 2800 Å. By the use of these spectra the H2O2 decomposition in the presence of H2 and CO at 870 ≤ T ≤ 1000°K has been analyzed. It was found that in this temperature range, in contrast to low temperature behavior, reactions of H atoms with H2O2 and with HO2 are equally important. The rate of the reaction H + H2O2 ← HO2 + H2 was estimated in comparison with the rate of the reaction between H and HO2. Good agreement between calculated and measured concentration profiles of HO2 and H2O2 was obtained.

Notes: The vibrational excitation of HF occurring behind incident shock waves has been studied in the temperature range of 1400°K to 4100°K. The extent of excitation was determined as a function of time by continuously monitoring the emission intensity from the 1-0 band of HF centered at 2.5 μ. The data were interpreted in terms of the process \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm HF}(0) + {\rm M = HF(1)} + {\rm M} $$\end{document} and gave a value of \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm (}\tau \rho {\rm)}\begin{array}{*{20}c} {{\rm - 1}} \\ {{\rm HF}} \\ \end{array}{\rm = 10}^{{\rm 9}{\rm .2} \pm 0.1} \exp \left({\frac{{- 64 \pm 4}}{{T^{1/3}}}} \right)atm^{- 1} \sec ^{- 1} $$\end{document} for M = HF. The corresponding result for (τp)-1Ar was found to be insignificant in comparison to this result. Data were also obtained for the effect of F atoms upon the relaxation rate, i.e., it was found that \documentclass{article}\pagestyle{empty}\begin{document}$$ {{\left( {\tau p} \right)_{{\rm HP}} } \mathord{\left/ {\vphantom {{\left( {\tau p} \right)_{{\rm HP}} } {\left( {\tau p} \right)_{\rm F} \sim 18 \pm 1}}} \right. \kern-\nulldelimiterspace} {\left( {\tau p} \right)_{\rm F} \sim 18 \pm 1}} $$\end{document}

Notes: 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 δH0f 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.

Notes: The competitive reactions between 2-trifluoromethylpropene (TMP) and OCS for O(3P) atoms were studied between 300° and 523°K, using the mercury-senstitized photolysis of N2O as a source of O(3P). From the known value for the rate constant of the O(3P) + TMP reaction, k3 was found to be 1.6 × 10-11 exp (-4500/RT) cm3/particle-sec, where reaction (3) is \documentclass{article}\pagestyle{empty}\begin{document}$${\rm (3) O(}^{\rm 3} {\rm P)} + {\rm OCS} \to {\rm CO} + {\rm SO}$$\end{document}Mixtures of O3 and OCS were photolyzed at 197°, 228°, 273°, and 299°K with radiation above 4300 Å to produce O(3P) from the photolysis of O3, and thus study the competition between reaction (3) and \documentclass{article}\pagestyle{empty}\begin{document}$${\rm (1)O(}^{\rm 3} {\rm P)} + {\rm O}_{\rm 3} \to 2{\rm O}_{\rm 2}$$\end{document} From the above value of k3, k1 could be computed. When combined with all the previous data, the best espression for k1 is k1 = 1.2 × 10-11 exp (-4300/RT) cm3/particle-sec.

Notes: An experimental study of the decomposition kinetics of chemically activated 2-methyl-l-butene and 3-methyl-l-butene produced from photolysis of diazomethane-isobutene-neopentane-oxygen mixtures is reported. The experimental rate constants for 3-methyl-l-butene decomposition were 1.74 ± 0.44 × 108 sec-1 and 1.01 ± 0.25 × 108 sec-1 at 3660 and 4358 Å, respectively. 2-Methyl-l-butene experimental decomposition rate constants were found to be 5.94 ± 0.59 × 107 sec-1 at 3660 Å and 3.42 ± 0.34 × 107 sec-1 at 4358 Å. Activated complex structures giving Arrhenius A-factors calculated from absolute rate theory of 1016.6 ± 0.5 sec-1 for 3-methyl-l-butene and 1016.2 ± 0.4 sec-1 for 2-methyl-l-butene, both calculated at 1000°K, were required to fit RRKM theory calculated rate constants to the experimental rate constants at reasonable E0 and E* values. Corrected calculations (adjusted E0 values) on previous results for 2-pentene decomposition gave an Arrhenius A-factor of 1016.45 ± 0.35 sec-1 at 1000°K. The predicted A-factors for these three alkene decompositions giving resonance-stabilized methylully radicals are in good internal agreement. The fact that these A-factors are only slightly less than those for related alkane decompositions indicates that methylallylic resonance in the decomposition products leads to only a small amount of tightening in the corresponding activated complexes. This tightening is a significantly smaller factor than the large reduction in the critical energy due to resonance stabilization.

Notes: The gas phase photolysis of CF3CCl3 in the presence of several alkanes has been used to obtain Arrhenius parameters for the abstraction of hydrogen atoms by the CF3CCl2 radical: \documentclass{article}\pagestyle{empty}\begin{document}$${\rm CF}_{\rm 3} {\rm CCl}_2 + {\rm RH} \to {\rm CF}_{\rm 3} {\rm CCl}_2 {\rm H} + {\rm R}$$\end{document}Activation energies of 9.6 and 8.0 kcal/mole are found for abstraction from secondary and tertiary C-H bonds, respectively. The Arrhenius parameters are compared to those for CCl3 and CF3 radicals.

Notes: The high-temperature reaction between sulfur dioxide and acetylene in an excess of argon was studied in a 1-in. i.d. single-pulse shock tube. Mixtures ranging from 1.81% to 5.40% SO2 and 1.60% to 4.90% C2H2 were heated to reflected shock temperatures of 1550°-2150°K, for dwell times of about 0.6 msec and gas dynamically quenched. Total reaction densities were 0.89 to 5.4 × 10-2 moles/1. The reaction products were analyzed by gas chromatography. A technique was developed for separating Ar, C2H4, C2H2, SO2, CO, CO2, H2S, COS, and CS2. The major products of the reaction are CO, H2, CS2, and sulfur. The products observed were compared with those predicted on the assumption that equilibrium was attained. Several preliminary experiments were carried out with ethylene-sulfur dioxide mixtures, and the results indicated that for this combination the sulfur dioxide probably reacted with the acetylene generated from the decomposition of the ethylene, rather than directly with the ethylene. The rate of decline in the sulfur dioxide content in C2H2-SO2 mixtures was found to be approximately second order (total) and can be empirically represented by \documentclass{article}\pagestyle{empty}\begin{document}$$- \Delta ({\rm SO}_2)/\Delta t = 3.1 \times 10^{10} T^{1/2} \exp (- 40,800/RT)[{\rm Ar}]^{0.83} [{\rm SO}_{\rm 2}]^{0.87} [{\rm C}_2 {\rm H}_{\rm 2}]^{0.25} {\rm mole cm}^{{\rm - 3}} \sec ^{ - 1}$$\end{document}A mechanism is proposed to account for the overall reaction kinetics.

Notes: C—Cl and C—C bond energies in the chloroethanes and C—H, C—Cl, and C—C bond energies in the chloroethyl radicals are calculated from known heats of formation of chloroethanes and chloroethylenes and known C—H bond energies in chloroethanes.The results obtained show a dependence of bond energy on the isomeric structure of the molecules and radicals and on the type of bond broken (primary, secondary, or tertiary). Heats of formation and bond energies estimated from group property additivity rules are in close agreement with experimental values.

Notes: A study of the pressure dependence of the C5 products from the reaction of cis-butene-2 and methylene is reported. Methylene was produced by the photolysis of diazomethane with 4358 Å light at 23° or 56°, and by photolysis of ketene with 3200 Å radiation at 23° or 100°. The change with increasing pressure of the relative amounts of the characteristically “triplet products” (trans-1,2-dimethylcyclopropane, trans-pentene-2 (TP2), and 3-methylbutene-1 (3MB1)) and “singlet products” (cis-1,2-dimethylcyclopropane (CDMC) and cis-pentene-2 (CP2)) are discussed. The behavior is reminiscent of that found in 3CH2-cis-butene-2 systems and can be interpreted in terms of the rapid rate of rearrangement of an initial triplet diradical product component, due to 3CH2, relative to the slower rate and readier collisional stabilization of an initial vibrationally-excited dimethyl cyclopropane product component, due to 1CH2. Relative rates of reactions of 1CH2 with allylic CH:vinyl CH:C=C in the neat liquid were, for diazomethane, 1:1.1:7.2 and, for ketene, 1:1.2:6.7.

Notes: The use of iodine monochloride (ICl) as a thermal source of chlorine atoms in known concentration is discussed with particular reference to the suppression, by large excesses of iodine, of the chain processes normally associated with chlorine atom reactions. The kinetics and mechanism of the reaction of ICl with hydrogen are presented in a study covering the temperature range 205-337°C, and the pressure ranges: ICl, 6-20 torr; I2, 3-13 torr; and H2, 9-520 torr. The reaction, followed spectrophotometrically in a static system, is shown to be homogeneous, first order in ICl and in H2, and inverse half-order in I2, over several half-lifetimes of the ICl, yielding HCl as the sole product. The rate data obtained in this work for the reaction are combined with the critically evaluated results of other workers in an Arrhenius plot covering the temperature range 286-730°C, and three orders-of-magnitude in the rate constant, yielding the results, log k1/(1/mole sec) = 10.68-5.26/θ, where θ = 2.303RT in kcal/mole. This value of k1 is lower by a factor of about two than that proposed in a recent review by Fettis and Knox, and is clearly at variance by a factor of two or more with the most recent data of Clyne and Stedman.

Notes: The temperature-jump method has been used to determine the nickel(II)- and cobalt(II)-arginine complexation kinetics. In the pH range studied, the neutral form of the ligand, HL, is the attacking, as well as the complexed, ligand species. The reactions reported on are of the type where n = 1, 2, 3 and M is Ni or Co. At 25° and ionic strength 0.1M the association rate constants are: for nickel(II) k1 = 2.3 × 103(±20%), k2 = 2.4 × 104(±20%), k3 = 3.5 × 104(±40%) M-1 sec-1; for cobalt(II) k1 = 1.5 × 105(±20%), k2 = 8.7 × 105(±20%), k3 = 2.0 × 105(±40%) M-1 sec-1. Arginine binds to metal ions less well than homologous chelating agents due to the electrostatic repulsion arising from the positively charged terminus of the zwitterion. Kinetically, the effect appears in the association rate constants with nickel reactions more strongly influenced than cobalt.

Notes: The spectrophotometric determination of the rate of iodine atom catalyzed geometrical isomerization of diiodoethylene in the gas phase from 502.8 to 609.1°K leads to a rate constant for the bimolecular reaction between I and trans-diiodoethylene of log kt-c(M-1 sec-1) = 8.85 ± 0.12 - (11.01 ± 0.30)/θ. Estimates of the entropy and enthalpy change for the addition of I atoms to trans-diiodoethylene (process a.b) lead to log Ka.b(M-1) = -2.99 - 4.0/θ, and thus to log kc (sec-1) = log kt-c - log Kab = 11.8 -7.0/θ for the rate constant for rotation about the single bond in the adduct radical. The theory for calculation of the rotation rate constant is presented and it is shown that while the exact value depends on the barrier height, a value of 6.8 kcal/mole for this quantity leads to log k (sec-1) = 11.8 -6.7/θ. The activation energy points to a better value of the group contribution to heat of formation of the group C-(I)2(H)(C) than one based on bond additivity.

Notes: The title reactions have been investigated in a fast flow system at pressures of about 2 torr and temperatures between 12 and 132°C. The following Arrhenius equations are derived for reaction (2) where the units of k2 are l/mole sec and of E2, cal/mole, and the limits are the 95% confidence limits assuming random errors.These equations are in good agreement with those which can be derived from previous investigations.

Notes: The reaction between carbon monoxide and atomic oxygen was studied in a gas flow over a temperature range of 136 to 230°C at atmospheric pressure. The rate constant of this reaction, considered to be one for a second-order reaction, was found to decrease with increasing temperature and to depend on the ratio of O2 to CO that was varied from 0.11 to 2.69. A conclusion was made that under the experimental conditions the reaction was third order The rate constant of this reaction was determined for a mixture of O2 and CO and it was found that the efficiency of O2 as particle M is four times that of CO.

Notes: Rates of solvolysis of benzyl chloride and of substituted benzyl chlorides have been measured in an acetone-water mixture (acetone mole fraction 0.147) at pressures ranging from atmospheric to 1 kbar. Pressure studies have also been made for p-methyl benzyl chloride in various acetone-water mixtures. Measurements have also been made of the partial molar volumes of the reactants. The plots of log k against pressure are fitted to a second-degree polynomial in P, and values of ΔV

Notes: The method of molecular-modulation spectrometry for studying photochemical reactions has been applied to methyl nitrite photolysis. The infrared absorption of the nitroxyl radical HNO has been observed in the gas phase at 3300 cm-1. Under the present experimental conditions the steady-state concentration of HNO under steady illumination was 1.1 × 1012 particles/cc, and the observed modulation amplitude was 4.5 × 1010 particles/cc. At 25°C and 1 atm of nitrogen, the cross section for infrared absorption by HNO at 3300 cm-1 is 1.7 × 10-19 cm2. The rate constant ratio b/c was found to be 8.0. From the literature value of the rate constant d , the observed rate constant for the reaction is e = (5 ± 1) × 10-11 cc/particle sec.

Notes: 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 (kA/sec-1) ≈ 12.5-46/θ would appear to be reasonable, while log (kB/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.

Notes: The thermal isomerization of the title compounds was studied in the vapor phase. Over the temperature range from 445.1 to 477.5°K, 1,4-dimethylbicyclo[2.2.0]hexane underwent a homogeneous unimolecular reaction to 2,5-dimethyl-1,5-hexadiene, the rate constants being represented by the equation: k = 1.86 × 1011 exp (-31000 ± 1800/RT) sec-1. Over the temperature range from 630.0 to 662.2°K, 1,4-dimethylbicyclo[2.1.1]-hexane also underwent a unimolecular isomerization to the same product, the rate constants being given by the equation: k = 8.91 × 1014 exp (-56000 ± 900/RT) sec-1. The pyrolysis of 1,4-dimethylbicyclo[2.1.0]pentane gave 1,3-dimethylcyclopentene-1 and 2,4-dimethyl-1,4-pentadiene in the ratio of 9:1. The former reaction was influenced by surface effects but the latter was not. The rate constants for the formation of 2,4-dimethyl-1,4-pentadiene fitted the equation: k = 1.66 × 1017 exp (-57400 ± 3100/RT) sec-1. The effect of the two methyl groups at the bridgehead positions in these molecules in influencing the rate of decomposition is discussed in terms of the non-bonded repulsive forces between the substituents.

Notes: Isotope effects, general acid catalysis, and relative reactivities show that proton transfer to one of the unsaturated carbon atoms is rate determining for the acidolysis of unsaturated alkylmercuric halides. For compounds, R1R2C=CHHgX, substitution of CH3 for H at R1 or R2 leads to an acceleration of a factor of ∼ 30. This relatively small acceleration, the relative facility of the reactions, and the magnitude of the Br- catalytic terms, suggests an olefin-mercuric halide complex as the product of the rate-determining step, rather than a simple carbonium ion.The Brøonsted catalysis law is obeyed with a variety of carboxylic acids, giving an ∝ of 0.69 ± 0.04, but acids of other structures give substantially deviant catalytic coefficients, in a pattern similar to that generated by other A-SE2 reactions. The acetic acid catalytic coefficient is larger by a factor of 102 than that predicted if it were due to specific hydronium ion-general base catalysis instead of true general acid catalysis.The overall solvent isotope effect, kH/kD, is 2.55 ± 0.10. The competitive isotope effect, κH/κD, is 6.84 ± 0.06. Taken with a model in which the proton is transferred directly from the H3O+ unit of the aquated proton to the substrate, these are sufficient to successfully predict the rate at all intermediate isotopic compositions.

Notes: The thermal decomposition of azomethane-d6 has been studied. There is a short chain reaction, and measurements have been made of the rate of production of N2, CD4, and C2D6. A mechanism is suggested which accounts for these results fairly well. A comparison is made with some similar results of Forst for azomethane. Measurements have also been made of the reaction inhibited by NO. It is believed that the N2 production, extrapolated to zero NO pressure, measures the rate of the initial step CD3N2CD3 → 2 CD3 + N2. This has an activation energy at high pressures of 50.7 kcal per mole and an Arrhenius A·factor of 1015.49 sec-1. This is to be compared to values of 55.5 and 1017.3 found by Forst and Rice for CH3N2CH3 → 2 CH3 + N2. The pressure fall-off behavior for CD3N2CD3 → 2 CD3 + N2 has also been investigated and compared to the theoretical curves, which seem to fit satisfactorily except at the lowest pressure, where experimental errors may be large. Unexpectedly, the fall-off curve crosses that for CH3N2CH3 → 2 CH3 + N2. It is suggested that the extrapolation to zero NO pressure may not be entirely correct in the CH3N2CH3 case where the chain is longer than with CD3N2CD3. It is believed that the decomposition of azomethane-d6 is a better example for unimolecular-rate theory than is that of azomethane.

Notes: t-Butylperoxy α-phenylisobutyrate (I) decomposes thermally by concerted formation of carbon dioxide, t-butoxy, and cumyl radicals. Radical pair return in the solvent cage therefore does not affect the observed rate of decomposition, but is readily determined by means of galvinoxyl and other scavengers. In a series of 15 solvents the rate constant varies over a 2.8 fold range, being fastest in aromatic solvents. In the same solvent series the relative rates of diffusion and combination of radicals, measured by the cage effect, change by tenfold and are largely determined by the viscosity of the solvent. In all solvents of η 〉 8 mP, the reciprocal of the cage effect is a linear function of (T1/2/η), as recently observed for trifluoromethyl and methyl radicals [16]. This property of the cage effect provides a test by which it can be distinguished from other processes that reduce the efficiency of free-radical production from an initiator.

Notes: The kinetics of ozonation of C2H4 and C2H2 have been studied in the gas phase from -40 to -95°C (C2H4) and +10 to -30°C (C2H2). The O3 concentrations were near 10-4 M, and the hydrocarbons were present in 2- to 25-fold excess. A few experiments with propylene were also carried out. The reactions were followed by observing the rate of decay of O3 absorption at 2537 Å. Reaction stoichiometries and effects of added O2 were investigated. The second-order rate constant for C2H4 was log k(M-1 sec-1) = (6.3 ± 0.2) - (4.7 ± 0.2)/θ (θ = 2.3RT). The rate was independent of the presence of excess O2. Rate measurements for C3H6 were less accurate because of aerosol interference. Combined with room temperature measurements of other workers, the C3H6 rate constant was log k(M-1 sec-1) = (6.0 ± 0.4) - (3.2 ± 0.6)/θ. The C2H2 rate constant was log k(M-1 sec-1) = (9.5 ± 0.4) - (10.8 ± 0.4)/θ. In the case of C3H6 the major product was propylene ozonide. Ethylene did not yield the ozonide, and the products of the O3-C2H4 and O3-C2H2 reactions were not identified. Pre-exponential factors for the olefin reactions are consistent with a five-membered ring transition state formed by 1,3 dipolar cycloaddition of O3. For C2H2, however, the much higher observed A factor suggests a different mechanism. Possible transition states for the O3-C2H2 reaction are discussed.

Notes: Methods are presented for rapidly estimating the entropies and heat capacities of free radicals from the known S0 and Cp0 of structurally similar compounds. The methods consist of estimating the differences due to changes in mass, vibration frequencies, spin, symmetry, and changes in rotational barriers. Tables of contributions to S0 and Cp0 by different frequencies over the temperature range 300-1500°K are presented to facilitate the tabulation of the above differences. Conjugated radicals, such as benzyl and allyl, are included. It is shown that the greatest uncertainties in the estimates arise from uncertainties in the barriers to rotation in the radicals.The results are applied to kinetic data on the pyrolysis of branched hydrocarbons and the reverse reactions of radical recombination. Major discrepancies exist in these data which can be nearly reconciled by postulating improbably high rotational barriers of 8 kcal for CH3 rotation in isopropyl and t-butyl radicals.It is shown that radical thermochemistry can be fitted into group schemes and tables of groups values are given for the rapid estimation of ΔHf0, S0, and Cp0 for different organic radicals, including those containing sulfur, oxygen, and nitrogen.

Notes: The rate of the reaction CH2I2 + HI ⇆ CH3I + I2 has been followed spectrophotometrically from 201.0 to 311.2°. The rate constant for the reaction fits the equation, log (k1/M-1 sec-1) = 11.45 ± 0.18 - (15.11 ± 0.44)/θ. This value, combined with the assumption that E2 = 0 ± 1 kcal/mole, leads to ΔHf298° (CH2I, g) = 55.0 ± 1.6 kcal/mole and DH298° (H—CH2I) = 103.8 ± 1.6 kcal/mole.The kinetics of the disproportionation, 2 CH3I ⇆ CH4 + CH2I2 were studied at 331° and are compatible with the above values.

Notes: Several hydrocarbons have been pyrolyzed in a single pulse shock tube. Rate parameters for the main bond breaking step have been found to be \documentclass{article}\pagestyle{empty}\begin{document}$$ k\left\{{{\rm iC}_3 {\rm H}_7 {-\!-} {\rm CH}\left({{\rm CH}_3} \right){\rm CH} {\raise1pt\hbox{$\Relbar \kern-4pt{\Relbar}$}} {\rm CH}_2 \longrightarrow {\rm iC}_3 {\rm H}_7 \cdot + \cdot {\rm CH}\left({{\rm CH}_3} \right){\rm CH} {\raise1pt\hbox{$\Relbar \kern-4pt{\Relbar}$}} {\rm CH}_2} \right\} = 10^{15.70} \exp \left({{{- 32,500} \mathord{\left/ {\vphantom {{- 32,500} T}} \right. \kern-\nulldelimiterspace} T}} \right)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k\left\{{{\rm iC}_3 {\rm H}_7 {-\!-} {\rm C}\left({{\rm CH}_3} \right)_2 {\rm C}_2 {\rm H}_5 \longrightarrow {\rm iC}_3 {\rm H}_7 \cdot + \cdot {\rm C}\left({{\rm CH}_3} \right)_2 {\rm C}_2 {\rm H}_5} \right\} = 10^{16.15} \exp \left({{{- 35,900} \mathord{\left/ {\vphantom {{- 35,900} T}} \right. \kern-\nulldelimiterspace} T}} \right)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k\left\{{{\rm C}_2 {\rm H}_5 {-\!-} {\rm C}\left({{\rm CH}_3} \right)_2 {\rm C}_2 {\rm H}_5 \longrightarrow {\rm C}_2 {\rm H}_5 \cdot + \cdot {\rm C}\left({{\rm CH}_3} \right)_2 {\rm C}_2 {\rm H}_5} \right\} = 10^{16.57} \exp \left({{{- 38,800} \mathord{\left/ {\vphantom {{- 38,800} T}} \right. \kern-\nulldelimiterspace} T}} \right)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k\left\{{{\rm iC}_3 {\rm H}_7 {-\!-} {\rm CH}_2 {\rm C}_6 {\rm H}_5 \longrightarrow {\rm iC}_3 {\rm H}_7 \cdot + \cdot {\rm CH}_2 {\rm C}_6 {\rm H}_5} \right\} = 10^{15.23} \exp \left({{{- 34,800} \mathord{\left/ {\vphantom {{- 34,800} T}} \right. \kern-\nulldelimiterspace} T}} \right)\sec ^{- 1} $$\end{document} In combination with similar studies carried out earlier and through application of the well-established experimental rule (kr2(AB)/kr(AA)kr(BB))1/2 ∼ 2 where A and B are radicals and the rate constants are for the combination of these radicals, rate parameters for the thermal decomposition of all the hydrocarbons formed from any pair of the following radicals: methyl, ethyl, isopropyl, t-butyl, t-amyl, allyl, methylallyl, and benzyl have been calculated. The available calculated and experimental values of the decomposition rate constants are in excellent agreement. It appears that, with the possible exception of reactions involving the ejection of methyl radicals, the frequency factors per bond are nearly constant, depending only upon the type of carbon-carbon bond that is being broken. These values are all lower than those expected from the radical recombination rates.Heats of formation of ethyl, t-amyl, benzyl, methylallyl, n-propyl, s-butyl, isobutyl, neopentyl, and 3-pentyl radicals have been derived.Rate parameters for the decomposition of some simple ketones and ethers have also been estimated.

Notes: The kinetics of the photoinitiated reductions of methyl iodide and carbon tetrachloride by tri-n-butylgermanium hydride in cyclohexane at 25°C have been studied and absolute rate constants have been measured. Rate constants for the combination of CH3ċ and CCl3ċ radicals are equal within experimental error and are also equal to the values found for the self-reactions of most non-polymeric radicals in low viscosity solvents, i.e. ∼1-3 × 109 M-1 sec-1.Rate constants for hydrogen atom abstraction by CH3ċ and CCl3ċ radicals are both ∼1-2 × 105 M-1 sec-1. Tri-n-butyltin hydride is about 10-20 times as good a hydrogen donor to alkyl radicals as is tri-n-butylgermanium hydride.The strength of the germanium-hydrogen bond, D(n-Bu3Ge-H) is estimated to be approximately 84 kcal/mole.

Notes: The kinetics of the thermally and radiation initiated chain reaction between trichloroethylene and cyclopentane to produce 1,1-dichlorovinylcyclopentane and hydrogen chloride have been investigated in the temperature range 250-360°C at high pressure in the gas phase. The rate governing step in the chain is (k3 = 3.3 × 109 exp -(4800/RT) cc mole-1 sec -1). The rate of the unimolecular decomposition of trichloroethylene is 1.4 × 1014 exp -(61,200/RT) sec-1.

Notes: The gas phase, nitric oxide catalyzed positional isomerization of 3-methylene-1,5,5-trimethylcyclohexene (MTC) into 1,3,5,5-tetramethyl-1,3-cyclohexadiene (TECD) has been studied for temperatures ranging between 296° and 425°C. The major reaction was first order with respect to nitric oxide and to MTC.The major side product, mesitylene, usually amounted to less than 10% of the TECD isomer formed. Only at high temperatures and large conversions has up to 20% been observed.Conditioned pyrex or quartz vessels coated with KCl have been used. The nitric oxide catalyzed isomerization is apparently a homogeneous process, as demonstrated by the insensitivity of the observed rate constants towards a 15-fold increase in the surface to volume ratio of the reaction vessels. However, a residual, presumably heterogeneous, thermal isomerization of the starting material could not be eliminated. Good mass balances were obtained for both NO and hydrocarbons.After correcting for the thermally induced conversion the observed rate constants for the nitric oxide catalyzed isomerization yield log k1 (1 mole-1 sec-1) = (10.7 ± 0.2) - (37.3 ± 0.9)/θ where θ is 2.303 × 10-3 RT (kcal mole-1). Plotting log k1 versus the ratio of the starting materials (MTC/NO)0 it was found that for temperatures ≥ 365°C the rate constants were systematically too high.Using extrapolated values for the higher temperature range yields the more reliable corrected Arrhenius equation log k1corr = 8.6 - 31.7/θ. The reaction mechanism is outlined and the implications with respect to the stabilization energy generated in the MTCċ radical intermediate and the activation energy of the backreaction MTCċ + HNO are discussed.Using for the activation energy E-1 of the backreaction (Rċ + HNO) a literature value of 9.2 ± 0.9 kcal mole-1 reported for the cyclohexadiene—1,3—system, this yields 23.4 ± 2 kcal mole-1 for the stabilization energy in the methylenecyclohexenyl radical, which is to be compared with the corresponding values for the allyl (10.2 ± 1.4), methallyl (12.6 ± 1) pentadienyl (15.4 ± 1) and cyclohexadienyl (24.6 ± 0.7) radicals.The pre-exponential factor agrees well with the value of (8.4 ± 0.2) reported by Shaw and co-workers for the similar reaction of NO with 1,3-cyclohexadiene. It is noteworthy that HNO, acting as sole hydrogen donor in the system, is surprisingly stable under the reaction conditions used. Nitrous oxide, HCN, H2O and N2 are observed in the product mixture of experiments carried out to high conversions at higher temperatures.

Notes: The following Arrhenius parameters have been determined for the hydrogen-abstraction reactions: R + (CH3)4Si → RH + (CH3)3SiCH3 TextRTemp. (°K)E (kcal/mole)Log A (mole-1 cc sec-1)Log k(400°K) (mole-1 cc sec-1)CF3330-4337.23 ± 0.0911.90 ± 0.057.95CH3396-47610.23 ± 0.3611.55 ± 0.185.68CD3396-49610.36 ± 0.1211.84 ± 0.066.20C2H5423-52211.40 ± 0.4811.88 ± 0.225.68The activation energies are in keeping with the strengths of the bonds formed during the reaction. By comparison with the activation energies for the analogous reactions of neopentane it is estimated that D((CH3)3SiCH2—H) ≃ 97 kcal/mole.The A factors for the above series of reactions fall within the range predicted by transition-state theory for this type of process and the validity of previous results of Kerr, Slater, and Young is seriously in doubt.

Notes: In the presence of elementary iodine, isobutyl iodide (2-methyl-1-iodopropane) undergoes isotopic exchange and also decomposes with production of additional iodine. Both reactions are approximately first order in isobutyl iodide and half order in iodine molecules. In degassed hexachlorobutadiene at 160°, the rate constants for exchange and decomposition are 7.5 × 10-6 and 11.4 × 10-6 (liter/mole)1/2sec-1, respectively. The decomposition is probably initiated by iodine atom abstraction of a β hydrogen atom, but comparison with rates for related compounds indicates that this hydrogen abstraction does not contribute significantly to the mechanism of exchange.

Notes: The kinetics and mechanism of the reaction between iodine and dimethyl ether (DME) have been studied spectrophotometrically from 515-630°K over the pressure ranges, I2 3.8-18.9 torr and DME 39.6-592 torr in a static system. The rate-determining step is, where k1 is given by log (k1/M-1 sec-1) = 11.5 ± 0.3 - 23.2 ± 0.7/θ, with θ = 2.303RT in kcal/mole. The ratio k2/k-1, is given by log (k2/k-1) = -0.05 ± 0.19 + (0.9 ± 0.45)/θ, whence the carbon-hydrogen bond dissociation energy, DH° (H—CH2OCH3) = 93.3 ± 1 kcal/mole. From this, ΔH°f(CH2OCH3) = -2.8 kcal and DH°(CH3—OCH2) = 9.1 kcal/mole.Some nmr and uv spectral features of iodomethyl ether are reported.

Notes: Arrhenius parameters have been determined for the hydrogen-abstraction reactions: R + SiHCl3 + RH + SiCl3 TextRTemp (°K)E(kcal/mole)Log A(mole-1 cc sec-1)Log k(400°K) (mole-1 cc sec-1)CF3323-4615.98 ± 0.0611.77 ± 0.038.50CH3333-4434.30 ± 0.0810.83 ± 0.044.48C2H5314-4135.32 ± 0.0711.54 ± 0.048.63The trend in activation energies ECH3 〈 EC2H5 〈 ECF3 is interpreted as indicating a polar effect in the reaction of CF3 with SiHCl3 and the similar reactivities of all three radicals appear to be due to the high exothermicity of the reactions.The A Factors for the reactions are normal for hydrogen abstraction reactions of free radicals. The previous results of Kerr, Slater, and Young for CH3 abstracting an H atom from SiHCl3 have been amended.

Notes: Stable nitroxide radicals and ESR techniques have been used to investigate rotational and translational motions of molecules in the liquid state. It is found that for hydrocarbons and molecules with low polarity the rotational frequencies are about an order of magnitude faster than translational encounters. Arrhenius parameters are reported for the rates of both types of processes. A scheme is given for the relation of these motions to radical recombination in solution and also to reactions requiring activation energy. The consequences of this scheme are examined.Such important properties as hydrodynamic fluidity, thermal conductivity, processes of extraction and solution, occurring in the liquid phase as well as at the interface are determined by mobility of particles in the liquid. The problem of molecular mobility is of essential significance for the kinetics of chemical and chemico-physical processes in the liquid phase.Application of both ESR techniques and stable nitroxide radicals for kinetic studies of molecular motions in liquids and the correlation between molecular mobility and the kinetic parameters of liquid-phase radical reactions have been studied in the present paper.

Notes: The photolysis of pentafluoroacetone has been investigated in the 3130 Å region, from room temperature to 360°C. The ΦCO varies from 0.7 to 0.9 over this range, and the decomposition is represented by CF2HCOCF3 → CF2H + CO + CF3. The disproportionation/combination ratio for CF3 and CF2H (→ CF3H + CF2) radicals is found to be 0.09. Arrhenius parameters for hydrogen atom abstraction from the ketone are log10A = 12.7 (units are mole-1 cc sec-1) and E = 14.3 kcal mole-1 for CF2H, and log10A = 12.1 and E = 11.8, for CF3 radicals. At low pressures HF elimination reactions are observed from the vibrationally excited fluoroethanes, C2F5H* and C2F4H2*, formed in the system. A rough estimate of the activation energy for the process C2F5H → C2F4 + HF of 60-65 kcal mole-1 is made.

Notes: The activating effects of a number of unsaturated groups and a cyclopropyl group have been evaluated in a solvent free system by determining the absolute rate constants, and energies and entropies of activation in the vapor phase pyrolysis of secondary and tertiary esters of the type RC(R′CH3) OAc where R′ = H or CH3 and R = c-Pr, i-Pr, CH3, CH2=CH, CH2=CHCH2, C6H5; the cyclopropyl showed only a moderate activating effect. The results are in contrast to the very significant activating effect of a cyclopropyl group in solvolysis of cyclopropylcarbinyl derivatives. Apparently marked activation by this group occurs only when a highly developed positive center forms adjacent to it. The lack of marked activation by the cyclopropyl group supports a mechanism for ester pyrolysis which involves a modest, but detectable, charge separation in the transition state [2] but questions a mechanism in which an intimate ion-pair was proposed [3].

Notes: The gas phase reaction I2 + HCOOCH3 → HI + CH3I + CO2 has been studied spectrophotometrically in a static system over the pressure ranges I2 (6-39 torr) and HCOOMe (28-360 torr). In the temperature range 293-356°, the initial rate of disappearance of I2 is first order in [HCOOMe] and half-order in [I2]. The rate determining step is where k1 is given by \documentclass{article}\pagestyle{empty}\begin{document}$$\log _{10} \left({k_1 /{\rm M}^{- 1} \sec ^{- 1}} \right) = \left({9.6 \pm 0.3} \right) - \left({22.4 \pm 0.8} \right)/\theta $$\end{document} where θ = 2.303 RT in kcal/mole. This activation energy gives a carbonyl C—H bond strength of 92.7 kcal/mole. At 356° there was no evidence of abstraction of a methoxy hydrogen, so a lower limit of 100 kcal/mole may be placed on this C—H bond strength. These ester C—H bond strengths are discussed in relation to comparable values in aldehydes and ethers.

Notes: The relative rates of addition of difluorocarbene to a series of methyl-substituted olefins have been determined and correlated with similar data for dichlorocarbene, chlorofluorocarbene and ground-state oxygen atoms. The electrophilic nature and stabilization of difluorocarbene by the fluorine substituents is discussed. Relative activation energies for the difluorocyclopropane-forming reaction have been estimated and correlated with properties of the olefins as derived from molecular orbital theory.

Notes: Data on the kinetics of S2F10 pyrolysis, which gives SF4 + SF6, have been reinterpreted to give a value for the equilibrium constant of S2F10 ⇆ SF4 + SF6. This, together with statistical estimates of the entropy and heat capacity of S2F10, can be used to give for this reaction values of ΔH298° = 19.7 ± 1.0 kcal/mole and ΔS300° = 47.6 ± 2 gibbs/mole. ΔHf°(S2F10) = -494 kcal/mole. A compatible mechanism is shown to be S2F10 ⇆ 2SF5 (fast); 2SF5 ⇆ SF6 + SF4 (slow) with step 2 rate-determining. The overall, best first order rate constant is proposed as kmeas = 1017.42-43.0/θ sec-1 = K1k2, where θ = 2.303RT in kcal/mole.Independent measurements of δHf° and S° for the SF5 radical, permits the evaluation of the equilibrium constant K1 = 108.92-(27.1 ± 6)/θ l./mole-sec and yields k2 = 108.50-15.9/θ l./mole-sec. The observed homogeneous catalysis by NO and CHCl = CHCl can be explained in terms of a direct abstraction of F from S2F10 : C + S2F10 → CF + S2F9, followed by S2F9 → SF5 + SF4 and SF5 + CF ⇆ SF6 + C (C ≡ NO or C2H2Cl2).

Notes: The gas phase isomerization of 1,1-dimethyl-2-vinylcyclopropane to cis-2-methylhexa-1,4-diene has been studied in a static system. The isomerization is homogeneous and kinetically first order. The rate constants were independent of initial reactant pressure in the range 0.6 to 2 torr and of added nitrogen up to 180 torr. Rate constants determined at 10 temperatures in the range 200 to 254°C fitted the Arrhenius equation k = 1011.41±0.02 exp (-33,540 ± 47 cal/RT) sec-1The low A factor and activation energy are consistent with a concerted 1,5-hydrogen migration via a “tight” cyclic transition complex.

Notes: The intramolecular elimination of isobutene from 2-d1-triisobutylaluminum has been studied in the gas phase for temperatures ranging between 102.4 and 184.6°C. The reaction is apparently homogeneous and obeys the first order rate law, yielding the following Arrhenius relationship: \documentclass{article}\pagestyle{empty}\begin{document}$$ \log \,k_{{\rm el}im} \left( {\sec ^{ - 1} } \right) = 11.1 - {{27.2} \mathord{\left/ {\vphantom {{27.2} {\theta \,{\rm where}\,\theta \,{\rm equals}\,4.58 \times 10^{ - 3} }}} \right. \kern-\nulldelimiterspace} {\theta \,{\rm where}\,\theta \,{\rm equals}\,4.58 \times 10^{ - 3} }}T\left( {{}^ \circ {\rm K}} \right)\,{\rm in}\,{\rm units}\,{\rm of}\,{{{\rm kcal}} \mathord{\left/ {\vphantom {{{\rm kcal}} {{\rm mole}{\rm .}}}} \right. \kern-\nulldelimiterspace} {{\rm mole}{\rm .}}} $$\end{document} Excess ethylene was added to the starting material in order to avoid complications from the backreaction. The cyclic 4-center nature of the transition state proposed earlier has been unequivocally demonstrated by deuterium labelling. Mass-spectral analyses show that the isobutene formed contains no deuterium. The hydrolyses products of the mixed trialkylaluminum formed during the reaction consist of monodeuteroethane and 2-d1-isobutane. The observed negative entropy of activation of ∼12 cal/°-mole agrees with prediction and implies a reasonably tight transition state structure. Combined with the corresponding data for the non deuterized Al(i-bu)3 reported earlier, these data result in a primary kinetic deuterium isotope effect of kH/kD = 1.3 × 100.6/θ corresponding to a ratio of the isotopic rate constants of 3.7 at 25°C. This result is in excellent agreement with a predicted value of 1.4 × 100.7/θ and it is in line with literature data on similar reactions involving cyclic transition state complexes.