Journal Article

Rehybridization dynamics into the pericyclic minimum of an electrocyclic reaction imaged in real-time

Saha, S. K., Hoffmann, M. C., Yang, J., Hegazy, K., Nunes, J. P. F., Liu, Y., Centurion, M., Shen, X., Champenois, E. G., Attar, A., Lin, M.-F., Sanchez, D. M., Martínez, T. J., Luo, D., Ware, M. R., Ji, F., Forbes, R., Wolf, T. J. A., Cryan, J. P., Wang, X. J.

2023

Overview

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. Electrocyclic reactions proceed through critical geometries, which are known as pericyclic transition states in thermal reactions and pericyclic minima in photochemical reactions. Here, the authors image the structure of a pericyclic minimum in real time using a combination of ultrafast electron diffraction and ab initio dynamics simulations.

• Publisher: Nature Publishing Group UK,Nature Publishing Group,Nature Portfolio
• Subject: 119/118 / 639/638/403/934 / 639/638/440/950 / 639/766/94 / ab initio multiple spawning / Carbon / Chemical bonds / chemical physics / Chemistry / Covalent bonds / electrocyclic reactions / Electron diffraction / Electrons / Excitation / Geometry / Humanities and Social Sciences / INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY / Internal conversion / Laboratories / multidisciplinary / Photochemical reactions / Photochemicals / photochemistry / Physics / reaction kinetics and dynamics / reaction mechanisms / Real time / Ring opening / Science / Science (multidisciplinary) / Simulation / Spheres / Terpinene / ultrafast electron diffraction / Wave packets