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

Abstract

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.

Photoreactions of cyclic sulfite esters: Evidence for diradical intermediates

“…As a consequence, the elimination of SO 2 results in a biradical BR2 with a conformation that is unfavorable for oxirane formation, but enables efficient hydrogen migration to result in aldehyde 3a . Theoretical calculations have confirmed that acetaldehyde derivatives may be formed upon rearrangement of the 1,3-oxyethandiyl [20–21] and that a subsequent decarbonylation results in an alkyl radical. The latter reaction yields bibenzyl ( 4 ) and toluene ( 7 ) in the photoreaction of 8 .…”

The Formation of DNA Photodamage: The Role of Exciton Localization

“…This approach has been used previously to describe photoreactions both in the gas phase and in the condensed phase, see for example refs. [28,29]. For these calculations the CPMD code [30] was employed with the BLYP density functional [31,32] and Troullier-Martins pseudopotentials [33] with a plane wave cutoff of 70 Rydberg.…”

Conservation of Orbital Symmetry can be Circumvented in Mechanically Induced Reactions

“…It has been shown previously, that it is not always possible to decide between different reaction paths solely on the basis of energy differences. [21] During the course of any reaction, the wavefunction has to change continuously in time, because otherwise it would not be differentiable with respect to time and thus violate a fundamental principle of quantum mechanics. Therefore the determination of the reaction mechanism may depend crucially on the evolution of the wavefunction.…”