Molecular Dynamics of Cope Rearrangements of Substituted 1,5-Hexadienes: Variable Transition States and Mechanisms

The Cope rearrangements of a variety of cyano- and phenyl-substituted derivatives have been studied with quantum mechanical calculations of potential energy surfaces with (U)M06-2<i>X</i>/6-311+G(d,p)//(U)B3LYP/6-31G(d) and molecular dynamics with (U)B3LYP/6-31G(d). The parent 1,5-hexadiene and 13 derivatives were explored. Mechanistic changes from concerted to stepwise - either associative or dissociative - are found, along with corresponding changes in timing of bond breaking and making, and formation of radical pairs in some highly substituted cases. Comparisons with experimental data in the literature and the analyses by Joseph J. Gajewski and William von Eggers Doering are provided.