Retro-cycloadditions and sigmatropic shifts: The C7H8 and C7H10 potential energy surfaces

Retro-cycloadditions and thermal rearrangements of hydrocarbons have been i nvestigated with density functional theory (B3LYP) and complete active spac e multiconfiguration self consistent field theory (CASSCF and CASPT2). We r eview recent results from our laboratories. Subjects are the laser-induced retro-Dids-Alder reactions of norbornene, thermal retro-Diers-Alder reactio ns of norbornenes and isopropylidenorbornene, 1,3-sigmatropic shifts of vin ylcyclopropane and bicyclo[3.2.0]heptenes, and the 1,5-sigmatropic shifts o f norcaradienes. The competition between concerted and stepwise processes a nd the nature of diradicals formed in these processes are described.