CARBONYL O-OXIDES AND DIOXIRANES - THE INFLUENCE OF SUBSTITUENTS ON SPECTROSCOPIC PROPERTIES

Triplet 4-oxocyclohexadienylidenes 6, matrix-isolated in Ar/2% O2 at 10 K, react with triplet O2 on annealing the matrix. Primary reaction products are quinone oxides 4, which have been characterized by IR and UV/Vis spectrometry. They are very photolabile; long-wavelength irradiation converts them into spiro-dioxiranes 5, which in turn yield lactones 10 upon irradiation with visible light. Experimental data have been obtained for quinone oxides 4 a - g; additionally, ground-state properties and UV/Vis absorptions of quinone oxides 4a, b and 4e-1 have been calculated by the MINDO-3/UHF and CNDO/S methods. Since the theoretical and experimental maxima of the pi --> pi* transitions are in good agreement, we conclude that our semiempirical calculations give an adequate picture of quinone oxides 4 which may best be described as dipolar diradicals.