摘要:

AbstractThe 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 × 1011exp (−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 × 1014exp (−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 × 1017exp (−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

ISSN:0538-8066    

DOI:10.1002/kin.550010202

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY

摘要:

AbstractThe 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−1sec−1) = 11.8–23.9/θ, where θ = 2.303RTin kcal/mole.It is suggested that a donor–acceptor complex intermediate may explain the observed rate constant of process B and analogous reacti

ISSN:0538-8066    

DOI:10.1002/kin.550010203

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY

摘要:

AbstractIsotope 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 CH3for H at R1or R2leads 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 102than 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

ISSN:0538-8066    

DOI:10.1002/kin.550010204

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY

摘要:

AbstractThe thermal decomposition of azomethane‐d6has 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 N2production, 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 ArrheniusA·factor of 1015.49sec−1. This is to be compared to values of 55.5 and 1017.3found by Forst and Rice for CH3N2CH3→ 2 CH3+ N2. The pressure fall‐off behavior for CD3N2CD3→ 2 CD3+ N2has 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 CH3N2CH3case where the chain is longer than with CD3N2CD3. It is believed that the decomposition of azomethane‐d6is a better example for unimolecular‐rate theory than i

ISSN:0538-8066    

DOI:10.1002/kin.550010205

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY

摘要:

Abstractt‐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

ISSN:0538-8066    

DOI:10.1002/kin.550010206

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY

摘要:

AbstractThe kinetics of ozonation of C2H4and C2H2have been studied in the gas phase from −40 to −95°C (C2H4) and +10 to −30°C (C2H2). The O3concentrations were near 10−4M, 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 O3absorption at 2537 Å. Reaction stoichiometries and effects of added O2were investigated. The second‐order rate constant for C2H4was logk(M−1sec−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 C3H6were less accurate because of aerosol interference. Combined with room temperature measurements of other workers, the C3H6rate constant was logk(M−1sec−1) = (6.0 ± 0.4) – (3.2 ± 0.6)/θ. The C2H2rate constant was logk(M−1sec−1) = (9.5 ± 0.4) – (10.8 ± 0.4)/θ. In the case of C3H6the major product was propylene ozonide. Ethylene did not yield the ozonide, and the products of the O3–C2H4and O3–C2H2reactions 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 observedAfactor suggests a different mechanism. Possible tra

ISSN:0538-8066    

DOI:10.1002/kin.550010207

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY

摘要:

AbstractMethods are presented for rapidly estimating the entropies and heat capacities of free radicals from the knownS0andC p0of 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 toS0andC p0by 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 CH3rotation in isopropyl andt‐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 ΔH f0,S0, andC p0for different organic radicals, including those containing sulfur, oxygen,

ISSN:0538-8066    

DOI:10.1002/kin.550010208

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY

摘要:

AbstractSeveral 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 (k r2(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

ISSN:0538-8066    

DOI:10.1002/kin.550010209

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550010210

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550010201

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY