On Electron Pair Rearrangements in Photochemical Reactions: 1,3-Cyclohexadiene Ring Opening

Abstract

1,3-Cyclohexadiene ring opening has been studied within the bonding evolution theory (BET) framework. We have focused on describing for the first time the electron pair rearrangements leading to the cis-1,3,5-hexatriene (HT) product from CHD. The nature of bonding in this process begins with the weakening of the double bonds in the Franck–Condon region. Along the 11B surface, the C–C sigma bond weakens. Meanwhile, its density redistributes toward the whole CHD ring, mainly over double bonds. Breaking of this bond occurs on the 21A surface due to the symmetrical splitting of pair density from this region. This density redistributes toward the reaction center once the pericyclic minimum is reached. The formation of the double bonds that characterize HT occurs gradually in the ground state. However, near the 21A/11A intersection, these bonds are partially established.

Photochemically Induced 1,3‐Butadiene Ring‐Closure from the Topological Analysis of the Electron Localization Function Viewpoint

“…Following such interests devoted to unraveling key bonding events occurring in photo-induced pericyclic reactions, we have concentrated recent interests on the usefulness of the so-called bonding evolution theory (BET). [22][23][24][25] BET [26] is based on the topology analysis of the electron localization function (ELF� h r ð Þ) [27,28] performed along a chosen reaction coordinate. [26,[29][30][31] ELF constitutes a measure of pair electron localization according to the Pauli-principle; in particular, the ELF gradient field, rh r ð Þ, provides a representation in terms of Lewis-like structures from its critical points (CPs).…”

“…Following ongoing interests [22][23][24][25] to further enhance our current knowledge of photochemical processes by exploiting the electron-pair approach, this work focuses on describing the reaction mechanism of one of the simplest photochemical pericyclic processes, namely the conversion of cis-1,3-butadiene (cis-BD) [44] into cyclobutene (CB), see scheme 1.…”

“…We aim to contribute to a deeper understanding of chemical bonding events in the electronically excited states. [22][23][24][25]…”

“…Following such interests devoted to unraveling key bonding events occurring in photo‐induced pericyclic reactions, we have concentrated recent interests on the usefulness of the so‐called bonding evolution theory (BET) [22–25] . BET [26] is based on the topology analysis of the electron localization function (ELF≡ ) [27,28] performed along a chosen reaction coordinate [26,29–31] .…”

“…We propose to study these details within the topological‐based framework offered by the BET. We aim to contribute to a deeper understanding of chemical bonding events in the electronically excited states [22–25] …”