Electrocyclic Ring Opening of 1 Alpha, 4 Alpha-and 1 Alpha, 4 Beta-Bicyclo(2.2.0)Hexa-2,5-Dienes ('Cis' and 'Trans' Dewar Benzenes): MNDO (Modified Neglect of Diatomic Overlap)Semiempirical Molecular Orbital Calculations.

摘要

Trans-Dewar benzene is calculated by the semi-empirical SCF-MO method MNDO to have a barrier of 21 kJ /Mole towards the allowed conrotatory electrocyclic ring opening to benzene, suggesting that the species may have a transient existence at low temperatures, while the forbidden disrotatory opening of cis-Dewar benzene is correctly predicted to involve passage over a much higher barrier via a transition state of C2 sub NU symmetry, (Author)