摘要:

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

ISSN:0538-8066    

DOI:10.1002/kin.550050102

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

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

ISSN:0538-8066    

DOI:10.1002/kin.550050103

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractThe photolysis of formamide vapor at 2062 Å has been studied in a flow system with results essentially similar to those obtained previously under static conditions and higher conversions. The rotating‐sector technique has been applied to the radical‐chain decomposition of formamide under conditions (305°C, 11.5 torr) such that decomposition of the carbamyl (NH2CO) radical was rate controlling, so that [NH2CO] ≫ [NH2]. A rate constant of (3.1 ± 1.0) × 1010(M·sec)−1was obtained for bimolecular chain termination by carbamyl radicals. A concurrent first‐order radical loss, probably at the surface, was taken into account by the treatment described by Shepp. Both oxamide and HNCO were tentatively identified as termination products, suggesting the occurrence of both combination and disproportionation,\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} 2{\rm NH}_2 {\rm CO} \to {\rm NH}_{\rm 2} {\rm CO} \cdot {\rm CO} \cdot {\rm NH}_{\rm 2} \\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, \to {\rm HNCO + NH}_{\rm 2} {\rm CHO} \\ \end{array} $$\end{document}but quantitative estimates of the relative rates were not possible. From the rate constant for chain termination, and relative rate constants obtained previously, Arrhenius parametersA∞= (5.9 ± 2.0) × 1012sec−1andA0= (1.04 ± 0.35) × 1014(M·sec)−1were estimated for the unimolecular decomposition of carbamyl radicals in the hig

ISSN:0538-8066    

DOI:10.1002/kin.550050104

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractThe reaction of hydrogen atoms with diazomethane was used as a source of methyl radicals to study the reaction of oxygen atoms with methyl radicals. This investigation verifies directly the earlier results that formaldehyde is a major product and that the rate constant is greater than 3×10−11cm3molecule−1s

ISSN:0538-8066    

DOI:10.1002/kin.550050105

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractThe very low‐pressure pyrolysis (VLPP) technique has been applied to the pyrolysis of di‐t‐amyl peroxide (DTAP) over the temperature range 523‐633°K. VLPP yields a low‐pressure rate constant,kuniThe conversion ofkunitok∞which must be made to calculate the Arrhenius parameters, is accomplished via the RRKM theory. The transition state model used in the RRKM calculations was based on a transition state model which accurately reproduced the VLPP data for di‐t‐butyl peroxide for which the Arrhenius parameters are well known. For the decomposition of DTAP it was found that logk∞(300°K) = 15.8 ‐ 36.4/θ, where θ = 2.303RT, in kcal/mole, and th

ISSN:0538-8066    

DOI:10.1002/kin.550050106

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractMethane is a primary product of pyrolysis of 3‐chloro‐l‐butene at temperatures in the range 776–835°K, and from its rate of formation values have been obtained for the limiting high‐pressure rate constant of the reactionThese may be represented by the expression log [(k1)∞/sec−1] = (16.7 ± 0.3) − (71.5 ± 1.5)/θ, where θ = 2.303RTkcal/mole. Assuming a zero activation energy for the reverse reaction and that over the experimental temperature range the rates at which a methyl radical adds on to chlorobutene are comparable to those at which it abstracts hydrogen, the activation energy for the dissociation reaction leads to a value of 83.2 ± 1.9 ckal/mole forD(HCHClCH:CH2) at 298°K. TakingD(HCHClCH2CH3) = 95.2 ± 1.0 kcal/mole a value of 12.0 ± 2.1 kcal/mole is obtained for the resonance energy of the chloroallyl radical. This value in conjunction with resonance energies obtained in earlier work indicates that substitution of a hydrogen atom on the carbon atom adjacent to the double bond in the allyl radical leads to no significant variation in

ISSN:0538-8066    

DOI:10.1002/kin.550050107

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractChemically activated ethane, with an excitation energy of 114.9 ± 2 kcal/mole, was formed by reaction with methane of excited singlet methylene radicals produced by the 4358 Å photolysis of diazomethane. A decomposition rate constant of (4.6 ± 1.2) × 109sec−1was measured for the chemically activated ethane. This result agrees, via RRKM theory, with most other chemically activated ethane data, and the result predicts, via RRKM and absolute rate theory forE0= 85.8 kcal/mole,E* = 114.9 kcal/mole, andkE= 4.6 × 101 sec−1, a thermalA‐factor at 600°K of 1016.6±0.2sec−1, in approximate agreement with the more recent experimental values. Combining 2 kcal/mole uncertainties inE0andE* with the uncertainty in our rate constant yields anA‐factor range of 1016.6±0.7sec−1. It is emphasized that this large uncertainty in theA‐factor results from an improbable combination of uncertainty limits for the various parameters. These decomposition results predict, via absolute rate theory (withE0(recombination) = 0) and statistical thermodynamic equilibrium constants, methyl radical recombination rates at 25°C of between 4.4 × 108to 3.1 × 109l.‐mole−1‐sec−1, which are 60 to 8 times lower, respectively, than the apparently quite reliable experimental value. A value ofE0(recombination) greater than zero offers no improvement, and a value less than zero would be quite unusual. Activated complexes consistent with the experimental recombination rate andE0(recombination) = 0 greatly overestimate the experimental chemical activation and high pressure thermal decomposition rate data. Absolute rate theory as it is applied here in a straightforward way has failed in this case, or a significant amount of internally consistent data are in serious error. Some corrections to our previous calculations for higher alka

ISSN:0538-8066    

DOI:10.1002/kin.550050108

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractWe have demonstrated that reactions for which substantial activation energies are needed can be induced to occur at room temperature via specific vibrational excitation. Indeed, the indications are that the atom‐switching reactions for whichEa>25 kcal take place with high probability only when the activation energy is localized in the vibrational mode. In this preliminary report on the utilization of the stimulated Raman effect to generate substantial populations in the critical vibrational states required for the homogeneous atom exchange between H2and D2, we first summarized the historical development of the concept. The experimental arrangement is then described and the analytical results tabulated; the observed dependence on relative concentrations is semiquantitatively rationalized on the basis of a model proposed in 1964. Independent shock tube and molecular beam investigations were similarly accounted for. Attention is called to the discrepancy between the generally concordant experimental results and theab initioquantum mechanical calculations of the potential energy surface for 4H atom

ISSN:0538-8066    

DOI:10.1002/kin.550050109

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractThe relative intensities of phosphorescence of SO2(3B1) molecules have been determined following the optical excitation of SO2(1B1) molecules by a 2662 Å laser pulse. From a kinetic treatment of these measurements, the intersystem crossing ratio,k2b/(k1b+k2b), was determined; SO2(1B1) + M → SO2(3B1) + M (2b); SO2(1B1) + M → SO2+ M (1b). With M = O2, N2, Ar, CO2, and CO,k2b/(k1b+k2b) = 0.030 ± 0.013, 0.034 ± 0.029, 0.025 ± 0.005, 0.052 ± 0.014, and 0.045 ± 0.028, respectively. These data allow a new, more quantitative evaluation of the extent of involvement of the “excess” triplet SO2in the 3130 Å‐irradiated mixtures of SO2and CO at high pressures [5, 6]. The new data are also of direct interest in the determination of the theoretical maximum rates of photooxidation of SO2in the sunlight‐irratiated atmos

ISSN:0538-8066    

DOI:10.1002/kin.550050110

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractThe initiated oxidation of 2, 4‐dimethylpentane in the neat liquid phase at 100°C with 760 torr O2gives more than 90% of a mixture of 2,4‐dihydroperoxy‐2,4‐dimethylpentane and 2‐hydroperoxy‐2, 4‐dimethylpentane in a ratio of 7:1. The rate of oxidation depends closely on the [initiator]1/2, consistent with a mechanism in which chain termination occurs mostly by interactions of two 2‐hydroperoxy‐2, 4‐dimethyl‐4‐pentylperoxy radicals. 2, 4‐Dimethylpentane oxidizes only one sixth as fast as isobutane at the same rate of initiation at 100°C. In cooxidations of the same hydrocarbons, it is 0.71 as reactive as isobutane toward any of the peroxy radicals involved. 2, 4‐Dimethylpentane oxidizes 7.5 times as fast at 1.25°C as at 50°C for the same rate of initiation, but the ratio of dihydroperoxide to monohydroperoxide increases only from 5 to 7, corresponding to a difference in activation energy between intramolecular and intermolecular abstraction of 1 kcal/mole. The overall activation energy (Ep–Et/2) is 10.7 kcal/mole, close to the value of 12 kcal/mole found for isobutane. Absolute values forEp,Et,kp,kr, andktwere derived. Ring closure of 2‐hydroperoxy‐2, 4‐methyl‐4‐pentyl radicals to oxetane, not detected during oxidation, was observed when this radical was generated at 100°C in the near‐absence of oxygen. The ratio of rate constants for oxetane formation and addition of oxygen to the 2, 4dimethyl‐2‐hydroperoxy‐4‐pentyl radical is about 5.4 × 10−5Mat 100°C. Thus, ring closure to oxetane is too slow to compete with addition of oxygen above ˜200 torr. At 100°C, 2, 3‐dimethylbutane gave no evidence of any intramolecular abstraction. However, 2, 3‐di

ISSN:0538-8066    

DOI:10.1002/kin.550050111

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY