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.

Genesis of rare molecules using light-induced reactions of matrix-isolated tetrazoles

“…Matrix isolation is a technique where gaseous atoms or molecules are commonly trapped in an environment of solidified noble gases at temperatures close to absolute zero (matrices can also be built from other gases; essentially inert, like N 2 , or even reactive like O 2 , for instance) [32][33][34][35][36]. Under these conditions, intramolecular rearrangements are inhibited for any process with an activation barrier larger than a few kJ mol −1 .…”

Photoinduced rotamerization and dissociation of o -fluorobenzoyl chloride in solid Ar

“…In the photolysis of benzoyl chloride in solid Ar, a ketene species (6-chloro-2,4-cyclohexadien-1-ylidenemethanone) was formed as an intermediate product followed by its dissociation to yield chlorobenzene and CO [6]. In contrast to the photolysis of benzaldehyde [7], the formation of a benzoyl radical was not confirmed.…”