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- Boman, Patrik, et al.
(author)
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Bond shift and charge transfer dynamics in methylene- and dimethylsilyl-bridged dicyclooctatetraene dianions
- 2001
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In: Journal of the Chemical Society Perkin Transactions 2. - : Royal Society of Chemistry (RSC). - 1472-779X .- 1364-5471. ; , s. 1130-8
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Journal article (peer-reviewed)abstract
- The rate constants for bond shift in dicyclooctatetraenylmethane (1), dicyclooctatetraenyldimethylsilane (2), and their dianions (12– and 22–) in [2H8]THF, have been determined from the temperature dependence of their 13C NMR linewidths. The corresponding parameters for intramolecular electron and cation transfer (charge transfer) between the dinegative and neutral rings have been measured by 13C NMR spin saturation transfer experiments for the dipotassium salts of 1 and 2. Selected structural features of the neutral compounds and the dianions are discussed on the basis of 13C NMR chemical shifts and ab initio molecular orbital calculations at the HF/6-31G* and HF/3-21G(*) levels of theory. Energy contributions to the ring flattening in the bond shift process are calculated by molecular mechanics methods. The measured rate constants for both bond shift and charge transfer are larger for the methylene-bridged dianion. Approximately half of this difference is due to the greater ease of gating (i.e., ring flattening and distortion to the bond shift transition state) in 12––2K+. A significant portion of the remainder is attributed to a greater inter-ring through-space interaction in 12–, although mediation by the cation and/or through-bridge interactions probably also contribute to some extent. A temperature-dependent differential 13C NMR line broadening is observed for the dianion ring carbons of the dipotassium salts. Possible mechanisms for this counterion-specific line broadening, which occurs only for carbons with large HOMO coefficients, are discussed.
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| 6. |
- Jonsson, Mats, 1967-, et al.
(author)
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Solvent Effects on Redox Properties of Radical Ions
- 1999
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In: Journal of the Chemical Society. Perkin Transactions 2 (2001). - : Royal Society of Chemistry. - 1472-779X .- 1364-5471. ; , s. 425-429
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Journal article (peer-reviewed)
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| 8. |
- Lindgren, M., et al.
(author)
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The [2H8]THF radical cation in CF3CCl3 and CFCl3 : an EPR and ENDOR study
- 1993
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In: Journal of the Chemical Society. Perkin Transactions 2 (2001). - 1472-779X .- 1364-5471. ; :11, s. 2009-2014
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Journal article (peer-reviewed)abstract
- The structure and dynamics of the radical cation of deuteriated tetrahydrofuran ([H-2(8)]THF) stabilized in the freon matrices CFCl3 and CF3CCl3 have been investigated by means of EPR and ENDOR spectroscopy. The EPR and ENDOR results of the rigid structure give two pairs of strongly interacting beta-deuterium hf splittings [a(D) = 1.36 (2 D) and a(D)) = 0.60 mT (2 D)] consistent with the protonated analogue [Kubodera et al., J. Phys. Chem., 1 981, 85, 2583 (ref. 1)]. An additional hf splitting (0.9-1.1 mT) assigned to the matrix fluorine was resolved above ca. 110 K in CFCl3. The temperature dependent EPR lineshapes (77-145 K) involving the exchange between four coupled (l = 1) nuclei have been analysed. A two-site model explained qualitatively the alterating line-widths at intermediate temperatures and resulted in an activation energy of ca. 1.7 kcal mol-1 A non-perturbative approach adopting a four-site model to account for puckering motion was tested. The dynamics were also manifested as a reversible temperature effect for the ENDOR. The relative abundance of resonances due to an averaged (hf) structure become predominant as the temperature is increased.
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