A carbon-13 NMR study of the ion pair structure of the dibenzo[b,f]pentalene dianion |
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Authors: | Bertil Eliasson Ulf Edlund |
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Abstract: | The 1H and 13C NMR chemical shifts of dibenzo[b, f]pentalene and its 5,10-dimethyl derivative are presented and compared with those of the corresponding dilithium dianions. As probed by the relative 13C NMR chemical shifts, the charge distribution within the dianion system is clearly dependent on the actual ion pair state. This condition is demonstrated by varying the solvent and temperature. The polarization of charge towards the pentalene carbons, i.e. the preferred cation positions, is observed on going to tight ion pair conditions. Further support for this model is gained from 7Li NMR. The limitations of the use of 1H and 13C NMR chemical shifts to measure charge distributions within anion systems are discussed. |
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