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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 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 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 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 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: 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: 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: This review presents in tabular and graphical form rate data on the reactions of atomic oxygen (O3P) with methane and ethane. The reliability of these data is discussed and suggested values of the rate constants are given over specified temperature intervals. Specific values are given for 298 and 1000°K.

Notes: A detailed kinetic model of the HCl chemical laser produced by the flash photolytically initiated H2—Cl2 explosion is described, and the results of computer calculations on such a system are discussed. It is shown that currently accepted values of the various rate constants, supplemented in a few cases by reasonable estimates of previously unmeasured rate constants, are adequate to approximate the observed laser behavior of this system. It is also shown that the chemistry of such a system is extremely complex, and exhibits a high degree of coupling between one reaction and another; therefore, great care is required to extract kinetic data from the optical behavior of such laser systems. It is further argued that different hydrogen halide lasers may behave quite differently from each other, depending on the relative magnitudes of the various rate constants involved.

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 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 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: 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: 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 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 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 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: 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: 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: 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: 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: 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 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.

Notes: The kinetics of the gas phase bond isomerization of allyl fluoride, allyl chloride and allyl bromide, catalyzed by HBr and ultraviolet light, has been studied in the temperature range of 150-250° and at pressures of 3.5 to 50 mm. The reactions are very clean, first order in allyl halide and HBr, and have a light intensity exponent of unity. A quantum yield for allyl chloride of 3200 indicates a chain reaction. Dilution with inert gases is almost without effect, indicating that excited state intermediates are not involved. A small wall effect is observed. The evidence indicates a free radical reaction, involving hydrogen abstractions by bromine atoms, with replacement at the other end of the allylic radical.

Notes: The thermal dissociation of COS was investigated in shock waves with argon as carrier gas. The concentration was varied between 0.05 and 0.5% COS in argon, the total density from 2.5 × 10-5 mole/cm3 to 2.5 × 10-3 mole/cm3. Temperatures between 1500°K and 3100°K were applied.For the reaction \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm COS}\left({^1 \Sigma} \right)\mathop {\longrightarrow}\limits^{K_{\rm 1}} {\rm CO}\left({^1 \Sigma ^ +} \right) + {\rm S}\left({^3 P} \right) $$\end{document} the rate constant was found to be \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{10} \approx 10^{14.2} \exp - \left({\frac{{61000}}{{RT}}} \right) \quad\quad ({\rm cm}^3 {\rm mole}^{- 1} \sec ^{- 1}) $$\end{document} in the low pressure range of the unimolecular reaction and \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{1\infty} \approx 10^{11.6} \exp - \left({\frac{{61000}}{{RT}}} \right) \quad\quad (\sec ^{- 1}) $$\end{document} in the high pressure range.

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: 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: 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: 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 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 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: By photolyzing (CF2H)2CO and (CFH2)2CO the hydrogen atom abstraction reactions of CF2H radicals with (CF2H)2CO, H2, D2, CH4, C2H6, n—C4H10 and iso—C4H10, and the reactions of CFH2 radicals with (CFH2)2CO and n—C4H10, have been studied. Arrhenius parameters for these reactions are compared with related systems. From a knowledge of the activation energies for the forward and reverse reactions a value of the bond dissociation energy, D(CF2H—H) = 97.4 ± 1.3 kcal mole-1 at a mean temperature of 543°K is obtained. This value is subject to much uncertainty due to possible compensation effects in the Arrhenius parameters. These effects are discussed for this and the other reactions, and the data suggest that D(CF2H—H) is approximately 100 kcal mole-1, and that D(CFH2—H) is very similar. Other literature data tend to confirm these approximate values.

Notes: The addition of methyl radicals to tetrafluoroethylene in the gas phase has been studied over the temperature range 80-180°C, using a material balance method. \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm CH}_{\rm 3} + {\rm C}_2 {\rm F}_{\rm 4} \to {\rm CH}_3 {\rm C}_2 {\rm F}_4 $$\end{document}Arrhenius parameters of 1011.95±0.23 (mole-1 cm3 sec-1) and 5.7 ± 0.4 (kcal/mole) have been measured for the addition reaction.Electrophilic reagents such as O or CF3 appear to react almost equally readily with ethylene and tetrafluoroethylene but methyl radicals add much more rapidly to tetrafluoroethylene than to ethylene, the difference in reactivity being principally due to an activation energy difference of ∼2 kcal/mole.