The Photochemistry of Carbon-Nitrogen Multiple Bonds in Aqueous Solution. 2. o-Hydroxy-Substituted Aromatic Oximes and Oxime Ethers

Article abstract of DOI:10.1021/jo00385a031

The fluorescence emission and excitation spectra of salicylaldoxime and o-hydroxyacetophenone oxime and several of their derivatives have been studied in various solvents.The results support the hypothesis that two major ground-state conformers exist, one having an intramolecular hydrogen bond ant the other being hydrogen bonded to solvent.Photolysis in aqueous solution occurs quite readily (Φ ca. 0.1-0.7) to give substituted benzoxazoles, although hydrolysis to give carbonyl product is competitive, especially in acidified solutions (Φ ca. 0.1-0.4).The cyclization reaction is believed to occur via two different mechanisms, arising from the inter- and intramolecularly hydrogen-bonded conformers, respectively.One mechanism involves cyclization via the phenolate ion, whereas the other is believed to involve intramolecular proton transfer to give a zwitteronic intermediate.