The photochemical Formation of Fulvene from Benzene via Prefulvene–a Theoretical Study

Abstract

Abstract:Results of semiempirical MN-DOC-CI and ab initio CASSCF calculations reveal that fulvene is a primary product of the photolysis of benzene. The photochemical step is assumed to lead to prefulvene, and both a synchronous conversion and a two-step process via bicyclo[3.1 .O]hexa-l,3-diene (isofulvene) could be ruled out as possible pathways from prefulvene to benzene. The most probable mechanism for the photochemi-and has to compete with the almost cal isomerization of benzene to fulvene in-barrierless formation of benzvalene and volves the intermediate structures pre-rearomatization to benzene. The shortfulvene and 1,3-~yclopentadienylcarbene lived intermediates are rather flexible structures with negligible barriers to inversion at the radical center in the threemembered ring of prefulvene and prebenzvalene and to rotation around the exocyclic single bond in 1,3-~yclopenta-dienyicarbene.

Infrared spectra and ultraviolet-tunable laser induced photochemistry of matrix-isolated phenol and phenol-d5

“…One of them is associated with the presence of a so-called prefulvene isomer, while the other is associated with the photodetachment of the hydrogen atom from the hydroxyl group. The existence of the prefulvenic reaction path has already been predicted 10 and observed 11 in benzene, while in phenol it has not been confirmed yet.…”

A comprehensive spectroscopic investigation of α-(2-naphthyl)-N-methylnitrone: a computational study on photochemical nitrone–oxaziridine conversion and thermal E–Z isomerization processes

“…[30][31][32] It will be quite interesting to investigate whether our presently targeted nitrone system also involve similar conical intersection topography during the oxaziridine formation step as the retinyl nitrones or not. This was found to have some similarity with the prefulvenic conical intersection in benzene which appears during its channel-3 decay.…”

Eine milde thermische Pentafulven‐Benzol‐Umlagerung

“…Die thermische Isomerisierung von Fulven, die 1972 zum ersten Mal von Henry und Bergman beschrieben wurde, findet wahrscheinlich über eine biradikalische “Präfulven”‐Zwischenstufe statt (Schema ) 3c. 5 Bislang wurden Pentafulven‐Benzol‐Umlagerungen nur nach den zwei benannten Methoden durchgeführt, was die Schwierigkeit dieser – zumindest auf Papier – einfachen Umlagerung aufzeigt. Als Teil unserer fortlaufenden Studien der 6,6‐Dicyanpentafulvene (DCF),6 einer Molekülklasse mit interessanten optoelektronischen Eigenschaften, fanden wir zufällig, dass nicht alle Pentafulvene solch harsche Bedingungen für die Umlagerung zum entsprechenden Benzolderivat erfordern.…”