The Isomerization of n-Pentyl and 4-Oxo-1-pentyl Radicals in the Gas Phase

Endrényi, László; Roy, D. J. Le

doi:10.1021/j100884a509

Cited by 42 publications

(33 citation statements)

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“…In addition to all of these considerations, intramolecular rearrangement of a primary to a secondary radical species is also know to occur. 46,47 STM images do not provide chemical information in any straightforward fashion; they reveal topography only, convoluted with the electronic structure of both the sample and the tip. While we observe a variety of structural changes in the octanethiolate monolayer as reaction with Cl proceeds, there is no simple a priori way to determine how to match each of the reaction products discussed above to a corresponding feature in an STM image.…”

Section: Pccp Papermentioning

confidence: 99%

The role of defects in the reaction of chlorine atoms with alkanethiol self-assembled monolayers

Lee

Jobbins

Gans

et al. 2013

Phys. Chem. Chem. Phys.

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Scanning tunneling microscopy (STM) in ultra-high-vacuum is used to investigate the reaction of gas-phase atomic chlorine with octanethiolate self-assembled-monolayers on Au(111). Exposure to Cl atoms results in the formation of a variety of surface defects, and eventually leads to a complete loss of order within the alkanethiolate monolayer. X-ray photoelectron spectroscopy and thermal desorption mass spectrometry show that these morphological changes are accompanied by significant chlorination of the monolayer as well as a ~30% decrease in the amount of adsorbed sulfur. The rate of reaction is measured through the analysis of sequences of STM images, and coverage-vs.-exposure data shows that the average reactivity of any given molecule within the monolayer decreases as the reaction progresses. Working with the assumption that monolayer defects created by Cl-atom reaction will affect the reactivity of neighboring molecules, a kinetic Monte Carlo simulation shows the data are consistent with defect sites inhibiting reaction rate by a factor of 5 or more. This behavior is opposite to that found for hydrogen-atom reactions, where edge and defect sites were far more reactive. The dynamics of chlorine-atom reactivity are described primarily in terms of the formation and subsequent reaction of surface-adsorbed radicals, with surface defects providing sites where these radicals can be quenched.

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Section: Pccp Papermentioning

confidence: 99%

The role of defects in the reaction of chlorine atoms with alkanethiol self-assembled monolayers

Lee

Jobbins

Gans

et al. 2013

Phys. Chem. Chem. Phys.

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“…If this excess p~-opene is attributed to reaction 3, then the rate constant for isomerization can be recalculated. Let R(.scc-pentyl products) = R,(i-C,H14) + A, and substitute it for R,(i-C6H,,) in the calculation of k7ki'2/k, (2). This has the effect on an Arrhenius plot of raising the high temperature (502 'K) rate constants by a factor of three, while leaving the low temperzture (438 OK) rate constant unchanged.…”

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confidence: 99%

“…The acetal group is stable towards basic conditions but it is extremely labile in the presence of mineral acids. Although it is usually believed that it is suitable for masking the carbonyl when a molecule is exposed to organometallic reagents, this is not always true (2,3). Thioacetals have been utilized only sporadically, mainly because they are obnoxious in smell, and more difficult to hydrolyze.…”

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confidence: 99%

On the Rate Constant for n-Pentyl Radical Isomerization

Watkins¹

1972

Can. J. Chem.

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A new interpretation of the mechanism used by Endrenyi and LeRoy for the calculation of the rate constant for 11-pcntyl isomeriza~ion is proposed. The addition of onc step to thc scheme makes possible a recalculation of the Arrhenius parameters. Significantly different values are found which eliminate the previously reported low A-factor. Canod~an Joulxal of Chcrnis[l.), SO, 3738 (1972) A discrepancy has long been recognized (1) pose into ethylene and ethyl radicals at about between the r e~o r t e d A-factors and those esti-157". mated from reasonable entropies of activation for the thermal isomerization of/?-pentyl(2) and 17-hexyl (3) radicals.The reported A-factors were about 10' s-', whereas the theoretical A-factors for 17-pentyl and 17-hexyl isomerization were estimated to be 1010.5-11 o s -l (lb, lc) and 101Os-l (4) respectively. The purpose of this communication is to suggest a resolution of this dilemma for 17-pentyl radical isomerization.In the case of isomerization of 17-pentyl radicals by 1,4-hydrogen atom migration. a reinterpretation of the original data of Endrznyi and LeRoy (2) suggests a suitable solution. These workers carried out their kinetic runs at temperatures between 165 and 230'. They assumed that the only reactions of .set-pentyl were isomerization back to n-pentyl, and combination with methyl. In other reports of 17-pentyl radical isomerization, both Gordon and McNesby (5) and Wijnen (6) observed that ,rec-pentyl radicals formed from 17-pentyl isomerization at 300' decomposed. Also, Morganroth and Calvert (7) in a study of the photolysis of 17-azobutane observed that il-butyl radicals began to decoinThis work proposes that in the calculations of Endrenyi and LeRoy a significant fraction of .set-pentyl radicals was not accounted for because they decomposed by reaction 3. A propene balance on their data (8) shows this suggestion to be a reasonable one. The three most important propene forming reactions (excluding 3) are Other reactions yielding C,H, can be imagined but their contribution is relatively unimportant. The rate of formation of propene fi-om these reactions can be estimated by the following expression where known o r estimated disproportionation to combination ratios can be used.R,(C,Hl,) is the rate of formation of 17-C,H14 from propyl radical combination. It is estimated from expression (iv) (8), kdj = A(n-Pr, n-Pr) = 0.15 (9); ki was estimated to be 0.04, from Can. J. Chem. Downloaded from www.nrcresearchpress.com by 54.245.13.81 on 05/11/18For personal use only.

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“…11,12 In these studies, the alkyl radicals are generally produced through either the photolysis or pyrolysis of alkyl azides, carbonyls, or halides. [11][12][13][14][15][16][17][18][19][20][21][22] Much of the early photolysis work on alkyl radical decomposition suffered from the determination of abnormally low reported A-factors that were in contention with the expected theoretical values. [13][14][15][16][17][18][19][20][21] Le Roy accounted for the discrepancy by including consideration for the effect of tunneling on the reaction pathways, which is significant for H-migration reactions at the low temperatures (o600 K) at which photolysis studies are conducted.…”

Section: Introductionmentioning

confidence: 99%

“…[11][12][13][14][15][16][17][18][19][20][21][22] Much of the early photolysis work on alkyl radical decomposition suffered from the determination of abnormally low reported A-factors that were in contention with the expected theoretical values. [13][14][15][16][17][18][19][20][21] Le Roy accounted for the discrepancy by including consideration for the effect of tunneling on the reaction pathways, which is significant for H-migration reactions at the low temperatures (o600 K) at which photolysis studies are conducted. 23 Pyrolysis studies, on the other hand, are typically performed at higher temperatures, and are therefore less affected by tunneling, though it still needs to be considered.…”

Section: Introductionmentioning

confidence: 99%

Ab initio study of chain branching reactions involving second generation products in hydrocarboncombustion mechanisms

Davis

Francisco

2012

Phys. Chem. Chem. Phys.

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sec-Alkyl radicals are key reactive intermediates in the hydrocarbon combustion and atmospheric decomposition mechanisms that are formed by the abstraction of hydrogen from an alkane, or as a second generation product of n-alkyl H-migrations, C-C bond scissions in branched alkyl radicals, or the bimolecular reaction between olefins and n-alkyl radicals. Since alkanes and branched alkanes, which the sec-alkyl radicals are derived from, make up roughly 40-50% of traditional fuels an understanding of their chemistry is essential to improving combustion systems. The present work investigates all H-migration reactions initiated from an sec-alkyl radical that involve the movement of a secondary hydrogen, for the 2-butyl through 4-octyl radicals, using the CBS-Q, G2, and G4 composite methods. The resulting thermodynamic and kinetic parameters are compared to similar reactions in n-alkyl radicals in order to determine underlying trends. Particular attention is paid to the effect of cis/trans and 1,3-diaxial interactions on activation energies and rate coefficients. When combined with our previous work on n-alkyl radical H-migrations, a complete picture of H-migrations in unbranched alkyl radicals is obtained. This full data set suggests that the directionality of the remaining branched chains has a minimal effect on the rate coefficients for all but the largest viable transition states, which is in stark contrast to the differences predicted by the structurally similar dimethylcycloalkanes. In fact the initial location of the secondary radical site has a greater effect on the rate than does the directionality of the remaining alkyl chains. The activation energies for secondary to secondary reactions are much closer to those of the secondary to primary H-migrations. However, the rate coefficients are found to be closer to the corresponding primary to primary reaction values. A significant ramification of these results is that there will be multiple viable reaction pathways for these reactions instead of only one dominant pathway as previously believed.

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The Isomerization of n-Pentyl and 4-Oxo-1-pentyl Radicals in the Gas Phase

Cited by 42 publications

References 0 publications

The role of defects in the reaction of chlorine atoms with alkanethiol self-assembled monolayers

The role of defects in the reaction of chlorine atoms with alkanethiol self-assembled monolayers

On the Rate Constant for n-Pentyl Radical Isomerization

Ab initio study of chain branching reactions involving second generation products in hydrocarboncombustion mechanisms

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