Utility of Chemical Indices for Transition Structures of Pericyclic Reactions: Case Study of the Cope Rearrangement

Stabilization effects of nonsynchronous transition structures (TSs) of the Cope rearrangements of phenyl-substituted 1,5-hexadienes were examined by the hybrid density functional theory (DFT) and UHF methods, Natural orbital analyses of the hybrid UDFT and UHF solutions were performed to analyze the instability of molecular orbitals at nonsynchronous TSs. It was found that the chemical characteristics at the TSs are made explicit in the behavior of the information entropy and related chemical indices, which are defined by the occupation numbers of natural orbitals. The computational results are discussed in connection with the utility of chemical indices and the applicability of the hybrid DFT methods for pericyclic reactions of large systems.