ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Near UV Spectroscopy and Electronic Structure of Dibenzo-p-dioxin, the Parent Compound of Highly Food-Polluting Agents

B. Vidal

Laboratoire de Chimie des Substances Naturelles et des Sciences des Aliments, Université de La Réunion, 97715-Saint-Denis messag. cedex 9 (La Réunion, France)

Received: 18 July 2001  Accepted: 6 November 2002

Abstract: Dibenzo- p -dioxinshows the first π-bond-order alternation observedwhen a six-membered ring is fused to a benzene moiety. This is particularlynoticeable because the presence of phenolic oxygens in the molecule, and anincreasing conjugation, should tend to quench alternation, when alternation is possible.Actually, oxygens tend to induce a quinodimethane-like structure. Alternationin dibenzo p-dioxin is explained firstly on the basis of that the two phenolicoxygens have to share their p_π - electronswith two benzene moieties, which decreases their effects towards each other. This limits their quenching ability. Alternation is explained secondly on thebasis of the fact that strain, which distorts the bridgehead bonds, inducingalternation, is increased compared to benzodioxan. Intensity calculations usingthe Interaction Vector Model, and the above electron-structure calculations, leadto results that fit with experiment. This shows that electron-structurebehaviour is understood.

Full paper in Portable Document Format: 572a112.pdf

Chemical Papers 57 (2) 112–118 (2003)