Rehybridization dynamics into the pericyclic minimum of an electrocyclic reaction imaged in real-time
Yusong Liu, David M. Sanchez, Matthew R. Ware, Elio G. Champenois, Jie Yang, J. Pedro F. Nunes, Andrew Attar, Martin Centurion, James Cryan, Ruaridh Forbes, Kareem Hegazy, Matthias C. Hoffmann, Fuhao Ji, Ming‐Fu Lin, Duan Luo, Sajib Kumar Saha, Xiaozhe Shen, Xijie Wang, Todd J. Martı́nez, Thomas Wolf
Abstract
Electrocyclic reactions are characterized by the concerted formation and cleavage of both σ and π bonds through a cyclic structure. This structure is known as a pericyclic transition state for thermal reactions and a pericyclic minimum in the excited state for photochemical reactions. However, the structure of the pericyclic geometry has yet to be observed experimentally. We use a combination of ultrafast electron diffraction and excited state wavepacket simulations to image structural dynamics through the pericyclic minimum of a photochemical electrocyclic ring-opening reaction in the molecule α-terpinene. The structural motion into the pericyclic minimum is dominated by rehybridization of two carbon atoms, which is required for the transformation from two to three conjugated π bonds. The σ bond dissociation largely happens after internal conversion from the pericyclic minimum to the electronic ground state. These findings may be transferrable to electrocyclic reactions in general.