Thermal Rearrangements of Norcaradiene

Multireference ab initio methods and density functional theory with a 6-31G* basis set have been applied to study the interconversions of norbornadiene, 1,3,5-cycloheptatriene, norcaradiene, and toluene. These include the [1,5]hydrogen shift in cycloheptatriene, the [1,5]carbon shift (walk rearrangement) in norcaradiene, the ring flip of cycloheptatriene, and the formation of norcaradiene from cycloheptatriene. Our best theoretical calculations for the walk rearrangement predict that the Woodward−Hoffmann “forbidden” suprafacial-inversion transition state and the “allowed” suprafacial-retention pathway differ in energy by