Tunneling in hydrogen-transfer isomerization of n-alkyl radicals.
Identifieur interne : 000847 ( Main/Curation ); précédent : 000846; suivant : 000848Tunneling in hydrogen-transfer isomerization of n-alkyl radicals.
Auteurs : Baptiste Sirjean [États-Unis] ; Enoch Dames ; Hai Wang ; Wing TsangSource :
- The journal of physical chemistry. A [ 1520-5215 ] ; 2012.
Abstract
The role of quantum tunneling in hydrogen shift in linear heptyl radicals is explored using multidimensional, small-curvature tunneling method for the transmission coefficients and a potential energy surface computed at the CBS-QB3 level of theory. Several one-dimensional approximations (Wigner, Skodje and Truhlar, and Eckart methods) were compared to the multidimensional results. The Eckart method was found to be sufficiently accurate in comparison to the small-curvature tunneling results for a wide range of temperature, but this agreement is in fact fortuitous and caused by error cancellations. High-pressure limit rate constants were calculated using the transition state theory with treatment of hindered rotations and Eckart transmission coefficients for all hydrogen-transfer isomerizations in n-pentyl to n-octyl radicals. Rate constants are found in good agreement with experimental kinetic data available for n-pentyl and n-hexyl radicals. In the case of n-heptyl and n-octyl, our calculated rates agree well with limited experimentally derived data. Several conclusions made in the experimental studies of Tsang et al. (Tsang, W.; McGivern, W. S.; Manion, J. A. Proc. Combust. Inst. 2009, 32, 131-138) are confirmed theoretically: older low-temperature experimental data, characterized by small pre-exponential factors and activation energies, can be reconciled with high-temperature data by taking into account tunneling; at low temperatures, transmission coefficients are substantially larger for H-atom transfers through a five-membered ring transition state than those with six-membered rings; channels with transition ring structures involving greater than 8 atoms can be neglected because of entropic effects that inhibit such transitions. The set of computational kinetic rates were used to derive a general rate rule that explicitly accounts for tunneling. The rate rule is shown to reproduce closely the theoretical rate constants.
DOI: 10.1021/jp209360u
PubMed: 22129143
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<record><TEI><teiHeader><fileDesc><titleStmt><title xml:lang="en">Tunneling in hydrogen-transfer isomerization of n-alkyl radicals.</title><author><name sortKey="Sirjean, Baptiste" sort="Sirjean, Baptiste" uniqKey="Sirjean B" first="Baptiste" last="Sirjean">Baptiste Sirjean</name><affiliation wicri:level="4"><nlm:affiliation>Department of Aerospace and Mechanical Engineering, University of Southern California, Los Angeles, California 90089-1453, USA. baptiste.sirjean@ensic.inpl-nancy.fr</nlm:affiliation><country xml:lang="fr">États-Unis</country><wicri:regionArea>Department of Aerospace and Mechanical Engineering, University of Southern California, Los Angeles, California 90089-1453</wicri:regionArea><orgName type="university">Université de Californie du Sud</orgName><placeName><settlement type="city">Los Angeles</settlement><region type="state">Californie</region></placeName></affiliation></author><author><name sortKey="Dames, Enoch" sort="Dames, Enoch" uniqKey="Dames E" first="Enoch" last="Dames">Enoch Dames</name></author><author><name sortKey="Wang, Hai" sort="Wang, Hai" uniqKey="Wang H" first="Hai" last="Wang">Hai Wang</name></author><author><name sortKey="Tsang, Wing" sort="Tsang, Wing" uniqKey="Tsang W" first="Wing" last="Tsang">Wing Tsang</name></author></titleStmt><publicationStmt><idno type="wicri:source">PubMed</idno><date when="2012">2012</date><idno type="doi">10.1021/jp209360u</idno><idno type="RBID">pubmed:22129143</idno><idno type="pmid">22129143</idno><idno type="wicri:Area/PubMed/Corpus">000078</idno><idno type="wicri:explorRef" wicri:stream="PubMed" wicri:step="Corpus" wicri:corpus="PubMed">000078</idno><idno type="wicri:Area/PubMed/Curation">000078</idno><idno type="wicri:explorRef" wicri:stream="PubMed" wicri:step="Curation">000078</idno><idno type="wicri:Area/PubMed/Checkpoint">000078</idno><idno type="wicri:explorRef" wicri:stream="Checkpoint" wicri:step="PubMed">000078</idno><idno type="wicri:Area/Ncbi/Merge">000223</idno><idno type="wicri:Area/Ncbi/Curation">000223</idno><idno type="wicri:Area/Ncbi/Checkpoint">000223</idno><idno type="wicri:Area/Main/Merge">000924</idno><idno type="wicri:Area/Main/Curation">000847</idno></publicationStmt><sourceDesc><biblStruct><analytic><title xml:lang="en">Tunneling in hydrogen-transfer isomerization of n-alkyl radicals.</title><author><name sortKey="Sirjean, Baptiste" sort="Sirjean, Baptiste" uniqKey="Sirjean B" first="Baptiste" last="Sirjean">Baptiste Sirjean</name><affiliation wicri:level="4"><nlm:affiliation>Department of Aerospace and Mechanical Engineering, University of Southern California, Los Angeles, California 90089-1453, USA. baptiste.sirjean@ensic.inpl-nancy.fr</nlm:affiliation><country xml:lang="fr">États-Unis</country><wicri:regionArea>Department of Aerospace and Mechanical Engineering, University of Southern California, Los Angeles, California 90089-1453</wicri:regionArea><orgName type="university">Université de Californie du Sud</orgName><placeName><settlement type="city">Los Angeles</settlement><region type="state">Californie</region></placeName></affiliation></author><author><name sortKey="Dames, Enoch" sort="Dames, Enoch" uniqKey="Dames E" first="Enoch" last="Dames">Enoch Dames</name></author><author><name sortKey="Wang, Hai" sort="Wang, Hai" uniqKey="Wang H" first="Hai" last="Wang">Hai Wang</name></author><author><name sortKey="Tsang, Wing" sort="Tsang, Wing" uniqKey="Tsang W" first="Wing" last="Tsang">Wing Tsang</name></author></analytic><series><title level="j">The journal of physical chemistry. A</title><idno type="eISSN">1520-5215</idno><imprint><date when="2012" type="published">2012</date></imprint></series></biblStruct></sourceDesc></fileDesc><profileDesc><textClass></textClass></profileDesc></teiHeader><front><div type="abstract" xml:lang="en">The role of quantum tunneling in hydrogen shift in linear heptyl radicals is explored using multidimensional, small-curvature tunneling method for the transmission coefficients and a potential energy surface computed at the CBS-QB3 level of theory. Several one-dimensional approximations (Wigner, Skodje and Truhlar, and Eckart methods) were compared to the multidimensional results. The Eckart method was found to be sufficiently accurate in comparison to the small-curvature tunneling results for a wide range of temperature, but this agreement is in fact fortuitous and caused by error cancellations. High-pressure limit rate constants were calculated using the transition state theory with treatment of hindered rotations and Eckart transmission coefficients for all hydrogen-transfer isomerizations in n-pentyl to n-octyl radicals. Rate constants are found in good agreement with experimental kinetic data available for n-pentyl and n-hexyl radicals. In the case of n-heptyl and n-octyl, our calculated rates agree well with limited experimentally derived data. Several conclusions made in the experimental studies of Tsang et al. (Tsang, W.; McGivern, W. S.; Manion, J. A. Proc. Combust. Inst. 2009, 32, 131-138) are confirmed theoretically: older low-temperature experimental data, characterized by small pre-exponential factors and activation energies, can be reconciled with high-temperature data by taking into account tunneling; at low temperatures, transmission coefficients are substantially larger for H-atom transfers through a five-membered ring transition state than those with six-membered rings; channels with transition ring structures involving greater than 8 atoms can be neglected because of entropic effects that inhibit such transitions. The set of computational kinetic rates were used to derive a general rate rule that explicitly accounts for tunneling. The rate rule is shown to reproduce closely the theoretical rate constants.</div></front></TEI></record>Pour manipuler ce document sous Unix (Dilib)
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