Source:http://linkedlifedata.com/resource/pubmed/id/15869291
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| Predicate | Object |
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| rdf:type | |
| lifeskim:mentions | |
| pubmed:issue |
18
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| pubmed:dateCreated |
2005-5-4
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| pubmed:abstractText |
In solution, the self-exchange reactions for oxygen-centered pi-radicals, e.g., PhO. + PhOH <==>PhOH + PhO., are known to occur with low activation enthalpies (E(a) approximately equal to 2 kcal/mol). For the PhO./PhOH couple and, we conclude, for other O-centered pi-radicals, exchange occurs by proton-coupled electron transfer (PCET) with the proton transferred between oxygen electron pairs while the electron migrates between oxygen orbitals orthogonal to the -O- - -H- - -O- transition state plane (Mayer et al. J. Am. Chem. Soc. 2002, 123, 11142). Iminoxyls, R(2)C=NO., are sigma-radicals with substantial spin density on the nitrogen. The R(2)C=NO./R(2)C=NOH self-exchange has a significant E(a) (Mendenhall et al. J. Am. Chem. Soc. 1973, 95, 627). For this exchange, DFT calculations have revealed a counterintuitive cisoid transition state in which the seven atoms, >C=NO- - -H- - -ON=C<, lie in a plane (R = H, Me) or, for steric reasons, two planes twisted at 45.2 degrees (R = Me(3)C). The planar transition state has the two N-O dipoles close to each other and pointing in the same direction and an O- - -H- - -O angle of 165.4 degrees . A transoid transition state for R = H lies 3.4 kcal/mol higher in energy than the cisoid despite a more favorable arrangement of the dipoles and a near linear O- - -H- - -O. It is concluded that iminoxyl/oxime self-exchange reactions occur by a five-center, cyclic PCET mechanism with the proton being transferred between electron pairs on the oxygens and the electron migrating between in-plane orbitals on the two nitrogens (R(N-N) = 2.65 A). The calculated E(a) values (8.8-9.9 kcal/mol) are in satisfactory agreement with the limited experimental data.
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| pubmed:language |
eng
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| pubmed:journal | |
| pubmed:status |
PubMed-not-MEDLINE
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| pubmed:month |
May
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| pubmed:issn |
0002-7863
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| pubmed:author | |
| pubmed:issnType |
Print
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| pubmed:day |
11
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| pubmed:volume |
127
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| pubmed:owner |
NLM
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| pubmed:authorsComplete |
Y
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| pubmed:pagination |
6693-9
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| pubmed:year |
2005
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| pubmed:articleTitle |
A theoretical study of the iminoxyl/oxime self-exchange reaction. A five-center, cyclic proton-coupled electron transfer.
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| pubmed:affiliation |
National Institute for Nanotechnology, National Research Council, 9107 116th Street, Edmonton, Alberta, Canada T6G 2V4. Gino.DiLabio@nrc.ca
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| pubmed:publicationType |
Journal Article
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