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Abstract
H/vinyl conical intersections are proposed to have a potential role in the photochemical hula-twist isomerization of hexatriene. The hula twist is a novel volume-conserving isomerization mechanism for polyenes in rigid media. Conical intersections involving partial migration of a hydrogen and inversion of a carbon are explored as potential pathways for hula-twist isomerization. These structures are geometrically ideal for a volume-conserving process, but are energetically unfavorable. Calculations were carried out using the complete active space self-consistent field (CASSCF) method and the 6-31G(d) basis set. Inclusion of electron correlation using CASPT2 calculations resulted in significant lowering of conical intersection energies. The structures and energetics of H/vinyl structures are compared and contrasted with kinked-diene structures and the conventional one-bond-flip process of cis–trans isomerization of tEt-hexatriene. The results are related to H/vinyl and kinked-diene conical intersections previously studied for butadiene.
Acknowledgements
We are grateful to the National Science Foundation for financial support of this research. This research was facilitated through the Partnerships for Advanced Computational Infrastructure (PACI) through the support of the National Science Foundation, and by the UCLA Academic Technology Services (ATS). J.E.N. would also like to acknowledge the Integrative Graduate Education and Research Traineeship program supported by the National Science Foundation at UCLA for financial support.