An absolute measurement of the rate constant for <i>t</i>‐butyl radical combination

Choo, Kwang Yul; Beadle, Peter C.; Piszkiewicz, L. W.; Golden, David M.

doi:10.1002/kin.550080107

Cited by 43 publications

(28 citation statements)

References 19 publications

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“…[5] does not represent the result of proper averaging of b + (~) over a Boltzman population. This latter is given by: [6] (bi(E)) = ]~* P ( E )~E 0 and using the appropriate P(E) (9)' we find: a result which differs from eq. [5] by about 1.5% A somewhat larger correction is found when we take the proper average of 2, over a Boltzman population.…”

Section: Introductionmentioning

confidence: 71%

“…What is most striking about these reactions is that they appear to have zero activation energy for both channels, recombination and disproportionation. Highly branched radicals such as tert-butyl appear to deviate from this general rule, showing a small decrease in rate of recombination with increasing temperature (6). Also striking about radical-radical reactions is that the rate constants generally fall between the limits of 1010.5 to L/mol-s, for all radical species.…”

Section: Introductionmentioning

confidence: 94%

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Molecular models for recombination and disproportionation of radicals

Benson¹

1983

Can. J. Chem.

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This paper is dedicated to Professor Harry E. G~trzrlirlg or1 the occn.sior1 of his 65th birthday SIDNEY W. BENSON. Can. J. Chem. 61, 881 (1983). The modified Gorin model of recombination as a long range interaction of weakly bound radicals, constrained only by steric forces, is rederived to give a collision impact parameter 11% larger than r,,,;,,, the separation at the centrifugal maximum. This larger impact parameter resolves some of the earlier difficulties with secondary and tertiary radicals. By imposing a new constraint, that the orientation of the radicals be such as to permit exchange forces to act, a new model is developed in which k , = 114 Z, a, where a represents the product of fractions of active surface areas of each radical available for bonding. Excellent agreement is obtained in estimating values of k,.Analysis of disproportionation is made to show that it cannot be described by the tight transition state but must also be governed by similar, long range exchange forces between the bond being attacked and the same "active surface" of the abstracting radical. Using an ad hoc radius for C'... H-C equal to 4 A it is possible to reproduce the data on alkyl radical disproportionation to within * 10%.The model predicts a small decrease in rate of recombination with increasing temperature. This decrease is more pronounced for bulkier radicals and at higher temperatures (>900 K). SIDNEY W. BENSON. Can. J. Chem. 61, 881 (1983). IOn a procCdt une nouvelle dCrivation du modele de recombinaison de Gorin modif6 en tant qu'interaction h longue distance des radicaux faiblement liCs et encombrCs uniquement par des forces steriques dans le but de donner un paramittre d'impact collisionnel de 11% supCrieur au r,,,,,,, la sCparation au maximum centrifuge. Ce plus grand parametre d'impact rCsoud quelques-unes des difficultks antkrieures rencontrkes avec les radicaux secondaires et tertiaires. En imposant une nouvelle contrainte, a savoir que ['orientation des radicaux doit Etre telle qu'elle permet aux forces d'Cchanges d'agir, on a mis au point un nouveau modkle dans lequel k , = 114 Z,a, ou a reprCsente le produit des fractions des surfaces actives de chaque radical disponible pour la liaison. On obtenu un excellent accord en Cvaluant k,.On a analysC la dismutation pour montrer qu'on ne peut pas la dCcrire par I'Ctat de transition intime mais qu'elle doit aussi &tre gouvernte par des forces d'Cchange a longue distance semblables entre le lien atttquC et la m&me "surface active" du radical qui provoque I'Climination. En utilisant un rayon "ad hoc" pour C'.-.H-C Cgal a 4 A, il est possible de reproduire les donntes relatives a la dismutation des radicaux alkyles avec une marge d'erreur de * 10%.Le modkle prCdit une ICgkre diminution de la vitesse de recombinaison quand la tempkrature augmente. Cette diminution est plus prononcCe pour les radicaux encombrCs et se manifeste des tempkratures plus ClevCes (>900 K).[Traduit par le journal] Introduction Transition State Theory permits us to model chemical reactions as th...

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Section: Introductionmentioning

confidence: 71%

Section: Introductionmentioning

confidence: 94%

Molecular models for recombination and disproportionation of radicals

Benson¹

1983

Can. J. Chem.

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“…However, since the compilation of data for groups, higher values of the heat of formation of t-butyl radicals have been determined [17,18]. …”

Section: Discussionmentioning

confidence: 99%

The azoethane‐initiated thermal reaction of isobutene. Heat of formation of the 2‐methyl‐2‐pentyl radical

Serés¹,

Görgényi²,

Farkaš³

1983

Int J of Chemical Kinetics

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The azoethane-sensitized thermal reaction of isobutene has been studied at 526-565 K.The initial concentrations of azoethane and isobutene were in the ranges of 1.40-10.5 X and 6.78-26.6 X mol/dm3, respectively. From the initial rates of formation of ethane and 2-methylpentane the heat of formation of the 2-methyl-2-pentyl radical was determined. The result obtained is q(2-methyl-2-pentyl) = 0.8 f 2.0 kcal/mol. The entropy of the radical, obtained from statistical mechanical calculations and experimentally, is S0(2-methyl-2-pentyl) = 92.8 f 1.5 cal/mol-K. The results support the high heat of formation of the t -butyl radical suggested by different authors.

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“…For the gas phase, Pd/PcE 2.8, independent of temperature within the considerable experimental scatter. Recent measurements in different laboratories [8] [9] point to a zero or small negative activation energy (-4 kJ . mol-') for the overall reaction rate constant k,.…”

mentioning

confidence: 99%