Mechanism of Electrocyclic Ring-Opening of Diphenyloxirane: 40 Years after Woodward and Hoffmann

• Published in: Chemistry : a European journal Vol. 15; no. 41; pp. 10825 - 10829
• Main Authors: Friedrichs, Jana, Frank, Irmgard
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 19.10.2009; WILEY‐VCH Verlag
• Subjects: density functional calculations; molecular dynamics; photochemistry; reaction mechanisms; ring-opening reactions
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200901152

The photochemistry of diphenyloxirane has been investigated by using static density functional theory and first‐principles molecular dynamics. We optimised potential‐energy surfaces for both the disrotatory and the conrotatory pathway in the first excited state. Although the disrotatory pathway does not seem to be favoured energetically, we get only the disrotatory product during the molecular dynamics simulations. This can be attributed to the “on‐the‐fly” description of the electronic structure in a first‐principles molecular dynamics simulation. The different photochemical behaviour of aryl oxiranes and unsubstituted oxirane is due to different shapes of the frontier orbitals. Woodward–Hoffmann revisited: The mechanism of the electrocyclic ring‐opening of oxirane depends on the nature of its substituents. Orbital analysis and first‐principles molecular dynamics simulations are performed to explain the differences between unsubstituted oxirane and diphenyloxirane by using the concept by Woodward and Hoffmann that as much bonding as possible should be maintained throughout the transformation.