AROYLNITRENES WITH SINGLET GROUND STATES: PHOTOCHEMISTRY OF ACETYL-SUBSTITUTED AROYL AND ARYLOXYCARBONYL AZIDES

Article abstract of DOI:10.1021/ja00221a032

The photochemistry of 4-acetylbenzoyl azide (ABA), 4-acetyl-4'-biphenoyl azide (ADA), and 4-acetylphenoxycarbonyl azide (APA) shows unusual wavelength and structrural effects.Irradiation of ABA or ADA into their ?-?^* bands with deep-UV light leads to formation of 4-acetylbenzoylnitrene (ABN) and 4-acetyl-4'-biphenylnitrene (ADN), respectively, in competition with photo-Curtis rearrangement to form isocyanates.Irradiation of these azides into their n-?^* bands with near-UV light gives only the aroylnitrenes.The triplet excited states of the azides were detected chemically and by transient spectroscopic techniques.Nitrogen loss following near-UV irradiation occurs exclusively from the excited triplet azides.However, the chemical properties of ABN and ADN are consistent only with reactions originating from their singlet states.An ESR spectrum is observed at 8 K for ((4-acetylphenoxy)carbonyl)nitrene (APN) but not for 4-acetylbenzoylnitrene (ABN) of 4-acetyl-4'-biphenylcarbonylnitrene (ADN).The chemical properties of APN in tert-butyl alcohol show that its triplet is no more than 5 kcal/mol below its lowest single state.In contrast, the chemical properties of ABN and ADN indicate that these niterenes have singlet ground states.