CYANOCARBENE, ISOCYANOCARBENE, AND AZACYCLOPROPENYLIDENE - A MATRIX-SPECTROSCOPIC STUDY

Matrix-isolated cyanoketene (5) was obtained by flash vacuum pyrolysis of the precursor 3 and by the photoinduced addition of carbon monoxid e to cyanocarbene (6), which was generated by irradiation of diazoacet onitrile (7), The reaction 6 --> 5 could be reversed by exciting 5 wit h UV light (lambda < 200 nm). Matrix-isolated 6 was isomerized to isoc yanocarbene (8) and azacyclopropenylidene (9) by irradiation with ligh t of selected wavelengths. The photochemical interconversions of the t hree C2HN isomers were completely reversible. The UV/Vis and IR spectr a of 8 and 9 are reported for the first time. The identification of bo th carbenes is based on the good agreement between the experimental an d theoretical IR spectra, which were obtained by density functional ca lculations (B3LYP/6-311 + + G*). From the IR spectra it can be conclu ded that 8 has a singlet ground state and a strongly bent structure.