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Investigation of molecular structures (EPR-Spectroscopy) | |
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Detailed knowledge of the electronic structure as well as the geometric shape of molecules can be obtained by electron paramagnetic resonance (EPR) spectroscopy. Our studies in this field are especially directed to the problem of intramolecular electron transfer. Electron denity distribution cannot easily be determinated by other experimental methods. They are, however, of considerable interest for organic chemistry since electron densities significantly influence chemical reactivities. Our studies are directed to molecules which consist of an aromatic core such as biphenyl,[1,2] napthalene,[3] anthracene,[4] phenanthrene,[4] fluorene,[1,2] azulene[5] or, especially, porphyrin[6] and its metal complexes, and one or several electron accepting substituents, e.g. ester, thioester[7,8] or nitro[2,4,6] groups. Radical anions are generated from the corresponding substrates by in-situ electroreduction. The hfs coupling constants obtained from the EPR spectra through simulation as well as their temperature and solvent dependence yield the desired information on the spin density distribution and intra- and intermolecular electron transfer processes. On the other hand, spin densities are also calculated by quantum chemical methods, e.g. density functional theory (DFT).[2,4,6]
References:
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[1] |
K. Osternack, Darstellung sterisch anspruchsvoller Biphenylderivate via Nickel(II)-Katalyse und EPR-spektroskopische Untersuchung der Radikalanionen von 3-(Oligophenyl)but-2-ensäureethylestern, Dissertation, Univ. Hamburg, 1996. |
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[2] |
S. Bruns, Dichtefunktional-theoretische Untersuchungen von EPR-Hyperfeinstrukturen am Beispiel der Radikalanionen von 4-Nitrobiphenyl und 9,9-Dimethyl-2-nitrofluoren, Diplomarbeit, Univ. Hamburg, 1998. |
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[3] |
K. Strey, J. Voss, J. Chem. Res., 1998 (S), 110-111; (M) 648-682. |
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[4] |
T. Behrens, Darstellung von tricyclischen, benzoiden Kohlenwasserstoffen mit elektronenanziehenden Substituenten und EPR-spektroskopische Untersuchung ihrer Radikalanionen, Dissertation, Univ. Hamburg, 1999. |
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[5] |
T. Pesel, Darstellung von Azulencarbonsäureestern und Azulenthiocarbonsäureestern sowie EPR-spektroskopische Untersuchung ihrer Radikalanionen, Dissertation, Univ. Hamburg, 1996. |
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[6] |
M. Schuler, Synthese, EPR-spektroskopische Untersuchungen und quantenmechanische Berechnungen der Radikalanionen von meso-substituierten Porphyrinen, Dissertation, Univ. Hamburg, 1998. |
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[7] |
J. Gassmann, H. Günther, K. Osternack, A. Sawluk, K. Thimm, J. Voss, Magn. Reson. Chem. 1994, 32, 624-630. |
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[8] |
J. Voss, T. Behrens, M. Krasmann, K. Osternack, L. Prangova, J. Chem. Res., 1997, 252-253. |
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