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Theoretical study on the Cope rearrangement mechanisms and the homoaromaticity of semibullvalene, barbaralane, and 1,5‐methanosemibullvalene
Author(s) -
Ichikawa Yuka,
Sakai Shogo
Publication year - 2012
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.1931
Subject(s) - excited state , chemistry , cope rearrangement , excitation , ab initio , symmetry (geometry) , ground state , transition state , atomic physics , molecular orbital , state (computer science) , computational chemistry , crystallography , stereochemistry , physics , molecule , quantum mechanics , catalysis , geometry , biochemistry , mathematics , organic chemistry , algorithm , computer science
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 C 2v 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 C 2v symmetry was not a transition state but one with a stable energy minimum. The energy minimum structure with C 2v symmetry had a biradical character. The lowest excited states of semibullvalene and barbaralane were the excitation to the σ* anti‐orbital, 1 B 2 and 1 B 1 states, and led to near di‐allyl states. The lowest excitation state of 1,5‐methanosemibullvalene had C s symmetry and was the A″ state excitation in one side of two allyl parts. Copyright © 2011 John Wiley & Sons, Ltd.