- Single Electron Transfer in Nucleophilic Aliphatic Substitution. Evidence for Single Electron Transfer in the Reactions of 1-Halonorbornanes with Various Nucleophiles
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A series of 1-halonorbornanes was used as a model system in reactions with several nucleophiles in order to determine the involvement of single electron transfer (SET) in nucleophilic aliphatic substitution in the absence of light.The 1-halonorbornanes were allowed to react with Me3Sn(1-), Ph2P(1-), AlH4(1-), N(iPr)2(1-), SPh(1-), and the 2-nitropropyl anion in the ether solvents at room temperature to 0 deg C.The results of product analyses, the use of radical and radical anion trapping reagents, the results of deuterium labeling studies, and the nucleofugality effect support a SET mechanism for the reactions involving 1-iodonorbornane.Convincing evidence that reduction of hindered alkyl iodides with LiAlH4 takes place by a SET pathway rather than by an impurity-initiated halogen atom radical chain process followed by an SN2 pathway, is presented.
- Ashby, E. C.,Sun, Xiaojing,Duff, J. L.
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- Acid-catalyzed cleavage of 4-halonortricyclanes. Evidence that the 2-norbornyl cation is an unsymmetrical species
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Nortricyclanes 4a, 4c, 4d, and 4e were prepared and ring opened in D2SO4/CD3COOD.We found that the ratios of endo/exo deuterium at C(6) were 1.09+/-0.02, 1.30+/-0.03, 1.40+/-0.04, and 1.45+/-0.05 for cleavage of 4a, 4c, 4d, and 4e, respectively.The amount of 6,2-hydride shift decreased from 14.3+/-1.0percent in the case of nortricyclane (4a) to 6.0+/-1.1percent, 6.4+/-0.5percent, and 8.1+/-0.7percent for 4c, 4d, and 4e, respectively.Although four distinct mechanisms involving either nonclassical or rapidly-equilibrating cations are possible, cleavage most probably occurs to generate 6,2-unsymmetrically-bridged norbornyl cations.
- Werstiuk, Nick Henry,Dhanoa, Daljit,Timmins, George
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p. 2403 - 2414
(2007/10/02)
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- Electron paramagnetic resonance of tetrakis(1-norbornyl)chromium
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Single-crystal epr of (nor)4Cr showed the molecule to have an isotropic g factor for the Δm = 1 transition. There were no Δm = 2 and double-quantum transitions; therefore D ≈ E ≈ O. In most organic glass these transitions become allowed. (nor)4Cr apparently assumes several conformations in isooctane and cyclohexane glasses which are distinguishable by their zero-field splitting parameters. Among all the solvents examined benzene perturbs the ligand field symmetry the least. Only a weak Δm = 2 signal was occasionally detected; there was no double-quantum transition even at highest available microwave power.
- Ward,Bower,Findlay,Chien, James C. W.
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p. 614 - 617
(2007/10/12)
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