Theoretical study on the Cope rearrangement mechanisms and the homoaromaticity of semibullvalene,barbaralane, and 1,5‐methanosemibullvalene |
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Authors: | Yuka Ichikawa Shogo Sakai |
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Institution: | Department of Chemistry, Faculty of Engineering, Gifu University, , Gifu, 501‐1193 Japan |
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Abstract: | Cope rearrangement mechanisms and the homoaromaticity of semibullvalene, barbaralane, and 1,5‐methanosemibullvalene in the ground and lowest excited states were studied by ab initio methods. In the ground state, the rearrangement reactions of semibullvalene and barbaralane occurred concertedly through the transition states with C2v symmetry, and the transition states had a homoaromatic nature. In particular, the transition state of barbaralane exhibited the strongest homoaromaticity among the three systems treated here. On the other hand, for 7,8‐methanosemibullvalene, the structure with C2v symmetry was not a transition state but one with a stable energy minimum. The energy minimum structure with C2v symmetry had a biradical character. The lowest excited states of semibullvalene and barbaralane were the excitation to the σ* anti‐orbital, 1B2 and 1B1 states, and led to near di‐allyl states. The lowest excitation state of 1,5‐methanosemibullvalene had Cs symmetry and was the A″ state excitation in one side of two allyl parts. Copyright © 2011 John Wiley & Sons, Ltd. |
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Keywords: | homoaromaticity mechanism |
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