Orbital topology. II. Orbital mapping of unsymmetrical molecules. A survey of the thermal isomerizations of dewar isomers of isoelectronically substituted benzenes,cyclopentadienes, and cyclopentadienyl ions

Orbital mapping analysis, based on EHT and CNDO/2 semiempirical molecular orbitals, has been used to survey the thermal, disrotatory, ring-opening isomerizations of bicyclo2.2.0]hexa-2,5-dienes (Dewar benzenes), bicyclo2.1.0]pent-2-enes, and bicyclo2.1.0]pent-2-en-5-yl ions to their planar isomers. Results indicate that isoelectronic substitution (CH replaced by C^?, O⁺, N, NH⁺, etc.) in the molecular framework may favor allowed thermal reactions in some cases, in contrast to the disallowed reaction predicted for the parent hydrocarbons.