Linear Free-Energy Relationships for the Alkyl Radical Affinities of Nitroxides: A Theoretical Study
Identifieur interne : 007764 ( Main/Exploration ); précédent : 007763; suivant : 007765Linear Free-Energy Relationships for the Alkyl Radical Affinities of Nitroxides: A Theoretical Study
Auteurs : Jennifer L. Hodgson [Australie] ; Ching Yeh Lin [Australie] ; Michelle L. Coote [Australie] ; Sylvain R. A. Marque [France] ; Krzysztof Matyjaszewski [États-Unis]Source :
- Macromolecules : (Print) [ 0024-9297 ] ; 2010.
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Abstract
High-level ab initio calculations have been used to construct linear free-energy relationships describing the kinetics and thermodynamics of the combination and dissociation reactions between alkyl radicals and nitroxides in terms of easily accessible parameters that quantify the electronic, steric and radical stabilization characteristics of the coreactants. For the gas-phase equilibrium constant (Keq = kc/kd) of the combination reaction at 298 K, the following equation was obtained: log (Keq) = -0.10IP - 0.177RSE -0.130RSEnxd + 38.3. In this equation, IP is the vertical ionization potential of the alkyl radical, RSE is the standard radical stabilization energy the alkyl radical, while RSEnxd is a new descriptor for the nitroxide radical, related to the standard radical stabilization energy, but measuring in this case the flexibility of the nitroxide to the geometric changes associated with formation of an alkoxyamine. The equation was successful for combinations of substituents not included in the original fitting and can thus be used to predict the behavior for larger systems for which direct calculation is impractical. Similar equations were also fitted to available experimental data for kc, at 298 K and kd, at 393 K, both in tert-butyl benzene, to allow the prediction of rate constants. The equation-determined rate constants, kc,eq and kd,eq are given by log (kc,eq) = -0.408IP - 0.0597RSE - 0.103RSEnxd + 14.5 and log (kd,eq) = 0.794IP + 5.68θ + 0.0873RSE + 0.0821RSEnxd - 27.7. For the decomposition rate, an additional parameter, Tolman's cone angle θ, which measures the steric bulk of the attacking alkyl radical, was found to improve the fit to the data. The equations could in principle be filled to experimental or calculated rate and equilibrium constants under a variety of reaction conditions. On the basis of our analysis, it appears that the stability of the alkyl radical has the largest effect on the kinetics and thermodynamics of the combination and dissociation reactions, with smaller but significant contributions from the remaining parameters.
Affiliations:
- Australie, France, États-Unis
- Pennsylvanie, Provence-Alpes-Côte d'Azur
- Marseille, Pittsburgh
- Université Carnegie-Mellon, Université de Provence
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Hodgson</name><affiliation wicri:level="1"><inist:fA14 i1="01"><s1>ARC Center of Excellence for Free-Radical Chemistry and Biotechnology, Research School of Chemistry, Australian National University</s1><s2>Canberra ACT 0200</s2><s3>AUS</s3><sZ>1 aut.</sZ><sZ>2 aut.</sZ><sZ>3 aut.</sZ></inist:fA14><country>Australie</country><wicri:noRegion>Canberra ACT 0200</wicri:noRegion></affiliation></author><author><name sortKey="Yeh Lin, Ching" sort="Yeh Lin, Ching" uniqKey="Yeh Lin C" first="Ching" last="Yeh Lin">Ching Yeh Lin</name><affiliation wicri:level="1"><inist:fA14 i1="01"><s1>ARC Center of Excellence for Free-Radical Chemistry and Biotechnology, Research School of Chemistry, Australian National University</s1><s2>Canberra ACT 0200</s2><s3>AUS</s3><sZ>1 aut.</sZ><sZ>2 aut.</sZ><sZ>3 aut.</sZ></inist:fA14><country>Australie</country><wicri:noRegion>Canberra ACT 0200</wicri:noRegion></affiliation></author><author><name sortKey="Coote, Michelle L" sort="Coote, Michelle L" uniqKey="Coote M" first="Michelle L." last="Coote">Michelle L. 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Hodgson</name><affiliation wicri:level="1"><inist:fA14 i1="01"><s1>ARC Center of Excellence for Free-Radical Chemistry and Biotechnology, Research School of Chemistry, Australian National University</s1><s2>Canberra ACT 0200</s2><s3>AUS</s3><sZ>1 aut.</sZ><sZ>2 aut.</sZ><sZ>3 aut.</sZ></inist:fA14><country>Australie</country><wicri:noRegion>Canberra ACT 0200</wicri:noRegion></affiliation></author><author><name sortKey="Yeh Lin, Ching" sort="Yeh Lin, Ching" uniqKey="Yeh Lin C" first="Ching" last="Yeh Lin">Ching Yeh Lin</name><affiliation wicri:level="1"><inist:fA14 i1="01"><s1>ARC Center of Excellence for Free-Radical Chemistry and Biotechnology, Research School of Chemistry, Australian National University</s1><s2>Canberra ACT 0200</s2><s3>AUS</s3><sZ>1 aut.</sZ><sZ>2 aut.</sZ><sZ>3 aut.</sZ></inist:fA14><country>Australie</country><wicri:noRegion>Canberra ACT 0200</wicri:noRegion></affiliation></author><author><name sortKey="Coote, Michelle L" sort="Coote, Michelle L" uniqKey="Coote M" first="Michelle L." last="Coote">Michelle L. Coote</name><affiliation wicri:level="1"><inist:fA14 i1="01"><s1>ARC Center of Excellence for Free-Radical Chemistry and Biotechnology, Research School of Chemistry, Australian National University</s1><s2>Canberra ACT 0200</s2><s3>AUS</s3><sZ>1 aut.</sZ><sZ>2 aut.</sZ><sZ>3 aut.</sZ></inist:fA14><country>Australie</country><wicri:noRegion>Canberra ACT 0200</wicri:noRegion></affiliation></author><author><name sortKey="Marque, Sylvain R A" sort="Marque, Sylvain R A" uniqKey="Marque S" first="Sylvain R. A." last="Marque">Sylvain R. A. Marque</name><affiliation wicri:level="4"><inist:fA14 i1="02"><s1>UMR 6264 Laboratoire Chimie Provence, case 521, Universite de Provence, Avenue Escadrille Normandie Niemen</s1><s2>13397 Marseille</s2><s3>FRA</s3><sZ>4 aut.</sZ></inist:fA14><country>France</country><wicri:noRegion>13397 Marseille</wicri:noRegion><placeName><settlement type="city">Marseille</settlement><region type="région" nuts="2">Provence-Alpes-Côte d'Azur</region><settlement type="city">Marseille</settlement></placeName><orgName type="university">Université de Provence</orgName></affiliation></author><author><name sortKey="Matyjaszewski, Krzysztof" sort="Matyjaszewski, Krzysztof" uniqKey="Matyjaszewski K" first="Krzysztof" last="Matyjaszewski">Krzysztof Matyjaszewski</name><affiliation wicri:level="4"><inist:fA14 i1="03"><s1>Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue</s1><s2>Pittsburgh, Pennsylvania 15213</s2><s3>USA</s3><sZ>5 aut.</sZ></inist:fA14><country>États-Unis</country><wicri:noRegion>Pittsburgh, Pennsylvania 15213</wicri:noRegion><orgName type="university">Université Carnegie-Mellon</orgName><placeName><settlement type="city">Pittsburgh</settlement><region type="state">Pennsylvanie</region></placeName></affiliation></author></analytic><series><title level="j" type="main">Macromolecules : (Print)</title><title level="j" type="abbreviated">Macromolecules : (Print)</title><idno type="ISSN">0024-9297</idno><imprint><date when="2010">2010</date></imprint></series></biblStruct></sourceDesc><seriesStmt><title level="j" type="main">Macromolecules : (Print)</title><title level="j" type="abbreviated">Macromolecules : (Print)</title><idno type="ISSN">0024-9297</idno></seriesStmt></fileDesc><profileDesc><textClass><keywords scheme="KwdEn" xml:lang="en"><term>Ab initio calculations</term><term>Alkyl radicals</term><term>Chemical coupling</term><term>Chemical reaction kinetics</term><term>Electronic effect</term><term>Free radical polymerization</term><term>Living polymer</term><term>MO method</term><term>Nitroxyl</term><term>Rate constant</term><term>Reversible reaction</term><term>Substituent effect</term><term>Theoretical study</term></keywords><keywords scheme="Pascal" xml:lang="fr"><term>Polymère vivant</term><term>Polymérisation radicalaire</term><term>Nitroxyle</term><term>Copulation chimique</term><term>Radical alkyle</term><term>Réaction réversible</term><term>Cinétique chimique</term><term>Constante vitesse</term><term>Effet substituant</term><term>Effet électronique</term><term>Calcul ab initio</term><term>Méthode MO</term><term>Etude théorique</term><term>Polymérisation médiée nitroxyle</term></keywords></textClass></profileDesc></teiHeader><front><div type="abstract" xml:lang="en">High-level ab initio calculations have been used to construct linear free-energy relationships describing the kinetics and thermodynamics of the combination and dissociation reactions between alkyl radicals and nitroxides in terms of easily accessible parameters that quantify the electronic, steric and radical stabilization characteristics of the coreactants. For the gas-phase equilibrium constant (K<sub>eq</sub> = k<sub>c</sub>/k<sub>d</sub>) of the combination reaction at 298 K, the following equation was obtained: log (K<sub>eq</sub>) = -0.10IP - 0.177RSE -0.130RSE<sub>nxd</sub> + 38.3. In this equation, IP is the vertical ionization potential of the alkyl radical, RSE is the standard radical stabilization energy the alkyl radical, while RSE<sub>nxd</sub> is a new descriptor for the nitroxide radical, related to the standard radical stabilization energy, but measuring in this case the flexibility of the nitroxide to the geometric changes associated with formation of an alkoxyamine. The equation was successful for combinations of substituents not included in the original fitting and can thus be used to predict the behavior for larger systems for which direct calculation is impractical. Similar equations were also fitted to available experimental data for k<sub>c</sub>, at 298 K and k<sub>d</sub>, at 393 K, both in tert-butyl benzene, to allow the prediction of rate constants. The equation-determined rate constants, k<sub>c,eq</sub> and k<sub>d,eq</sub> are given by log (k<sub>c,eq</sub>) = -0.408IP - 0.0597RSE - 0.103RSE<sub>nxd</sub> <sub>+</sub> 14.5 and log (k<sub>d,eq</sub>) = 0.794IP + 5.68θ + 0.0873RSE + 0.0821RSE<sub>nxd </sub>- 27.7. For the decomposition rate, an additional parameter, Tolman's cone angle θ, which measures the steric bulk of the attacking alkyl radical, was found to improve the fit to the data. The equations could in principle be filled to experimental or calculated rate and equilibrium constants under a variety of reaction conditions. On the basis of our analysis, it appears that the stability of the alkyl radical has the largest effect on the kinetics and thermodynamics of the combination and dissociation reactions, with smaller but significant contributions from the remaining parameters.</div></front></TEI><affiliations><list><country><li>Australie</li><li>France</li><li>États-Unis</li></country><region><li>Pennsylvanie</li><li>Provence-Alpes-Côte d'Azur</li></region><settlement><li>Marseille</li><li>Pittsburgh</li></settlement><orgName><li>Université Carnegie-Mellon</li><li>Université de Provence</li></orgName></list><tree><country name="Australie"><noRegion><name sortKey="Hodgson, Jennifer L" sort="Hodgson, Jennifer L" uniqKey="Hodgson J" first="Jennifer L." last="Hodgson">Jennifer L. Hodgson</name></noRegion><name sortKey="Coote, Michelle L" sort="Coote, Michelle L" uniqKey="Coote M" first="Michelle L." last="Coote">Michelle L. Coote</name><name sortKey="Yeh Lin, Ching" sort="Yeh Lin, Ching" uniqKey="Yeh Lin C" first="Ching" last="Yeh Lin">Ching Yeh Lin</name></country><country name="France"><region name="Provence-Alpes-Côte d'Azur"><name sortKey="Marque, Sylvain R A" sort="Marque, Sylvain R A" uniqKey="Marque S" first="Sylvain R. A." last="Marque">Sylvain R. A. Marque</name></region></country><country name="États-Unis"><region name="Pennsylvanie"><name sortKey="Matyjaszewski, Krzysztof" sort="Matyjaszewski, Krzysztof" uniqKey="Matyjaszewski K" first="Krzysztof" last="Matyjaszewski">Krzysztof Matyjaszewski</name></region></country></tree></affiliations></record>Pour manipuler ce document sous Unix (Dilib)
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