Absolute configuration of chiral [2.2]paracyclophanes with intramolecular charge-transfer interaction. Failure of the exciton chirality method and use of the sector rule applied to the cotton effect of the CT transition |
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Authors: | Furo Takahiro Mori Tadashi Wada Takehiko Inoue Yoshihisa |
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Institution: | Department of Molecular Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita 565-0871, Japan. |
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Abstract: | Optically active 4,7-dicyano-12,15-dimethoxy2.2]paracyclophanes have been separated by chiral HPLC and their absolute configurations determined by comparison of the experimental and the theoretical VCD spectra. X-ray crystallographic structures for both diastereomers are also reported. The electronic circular dichroism spectra of these enantiomeric pairs, as chiral intramolecular charge-transfer complexes, have been obtained for the first time. The exciton coupling method, usually used for determining the absolute configuration of chiral molecules, however, did not give a correct prediction for the present CT-paracyclophane system. Instead, empirical sector rules for the signs of the Cotton effects of the CT transition can be applied for the assignment of the absolute configuration. |
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