ORGN 117 |
| We report the electrochemistry of a series of meta and para-substituted benzylidenefluores. Oxidation of meta and para substituted benzylidenefluorenes would be expected to form antiaromatic cations while reduction would give aromatic dianions. NMR spectroscopy and electrochemistry were used for the evaluation of the antiaromaticity or aromaticity of the diions. This data was compared to calculated nucleus independent chemical shifts(NICS) that showed that the dications were antiaromatic while the dianions were aromatic. Electron withdrawing substituents, which would stabilize the dication, increased the antiaromaticity, as evaluated through NICS and through changes in the redox potential indicating decreased stability. Electron donating substituents had the opposite effect. The meta-substituted benzylidenefluorenes were found to be more antiaromatic than the para-ones through NICS calculations. However, m-substituted benzylidenefluorenes did not exhibit proper redox peaks, in contrast to the behaviour of the p-substituted benzylidenefluorenes that is consistent with their greater antiaromaticity. The corresponding redox peaks were well defined for the dianions and the redox potential values lower indicating the ease of reduction to dianion and their stability based on the peak current ratios. Enhanced stability is expected for aromatic species. Redox potentials varied with the nature of the substituents. |
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Asymmetric Reactions and Syntheses, Physical Organic Chemistry, Combinatorial Chemistry, Total Synthesis
8:00 PM-10:00 PM, Sunday, 26 March 2006 Georgia World Congress Center -- Ex. Hall B4, Poster
Division of Organic Chemistry |