REACTIONS OF UNSATURATED AZIDES .11. DIRECT OBSERVATION OF 2-METHYLENE-2H-AZIRINE

2-Methylene-2H-azirine (3a) was generated by photolysis of azidopropad iene (2a) and characterized by low-temperature H-1 NMR spectra and IR data of the matrix-isolated substance. Ab initio calculations at the M P2/6-31+G//MP2/6-31+G* level are reported for 3a as well as for 3-met hyl-2-methylene-2H-azirine (3b) and are in good agreement with the exp erimental results. This is shown by comparison of computed versus meas ured IR spectra of the azatriafulvenes 3a and 3b. The contribution of a dipolar canonical structure to the resonance hybrid of 3, which is t he first example of a heterocyclic triafulvene, is discussed.