title: Using heavy atom rare gas matrix to control the reactivity of 4-methoxybenzaldehyde: a comparison with benzaldehyde.
abstract: Different patterns of photochemical behavior were observed for 4-methoxybenzaldehyde (p-anisaldehyde) isolated in xenon and in argon matrices. Monomers of the compound isolated in solid Xe decarbonylate upon middle ultraviolet irradiation, yielding methoxybenzene (anisole), and CO. On the other hand, p-anisaldehyde isolated in an Ar matrix and subjected to identical irradiation, predominantly isomerizes to the closed-ring isomeric ketene (4-methoxycyclohexa-2,4-dien-1-ylidene) methanone. Experimental detection of a closed-ring ketene photoproduct, generated from an aromatic aldehyde, constitutes a rare observation. The difference between the patterns of photochemical transformations of p-anisaldehyde isolated in argon and xenon environments can be attributed to the external heavy-atom effect, where xenon enhances the rate of intersystem crossing from the singlet to the triplet manifold in which decarbonylation (via p-methoxybenzoyl radical) takes place. The parent compound, benzaldehyde, decarbonylates (to benzene + CO) when subjected to middle ultraviolet irradiation in both argon and xenon matrices. This demonstrates the role of the methoxy p-anisaldehyde substituent in activation of the reaction channel leading to the formation of the ketene photoproduct.
authors.affiliation: Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal.
authors.forename: Nihal
authors.initials: N
authors.lastname: Kuş
authors.forename: Archna
authors.initials: A
authors.lastname: Sharma
authors.forename: Igor
authors.initials: I
authors.lastname: Reva
authors.forename: Leszek
authors.initials: L
authors.lastname: Lapinski
authors.forename: Rui
authors.initials: R
authors.lastname: Fausto