Spectral, Structural, and Theoretical Considerations

As the major spectral, structural, and theoretical features of arylnitrenes have been dealt with at some length in previous reviews only salient points of older work will be stated here. 

Instead, an intense absorption at 1895 cm was observed and attributed to 1-aza-l,2,4,6-cycloheptatetraene (13). Irradiation of a-azidostyrene (14) under the above conditions with light of wavelength above 336 nm gave the azirine (15) 

The implications for this intermediate in the mechanism of arylnitrene ring expansions will be discussed later. Only structural considerations will be dealt with here to try to help rationalize why the apparently much less stable intermediate l-aza-l,2,4,6-cycloheptatetraene should be favored over benzazirine. Chapman has proposed the VB (13) and MO (17-18) structures for 1-aza-1,2,4,6-cycloheptatetr aene. 

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