Iminopropadienones RN=C=C=C=O and bisiminopropadienes RN=C=C=C=NR: Matrix infrared spectra and anharmonic frequency calculations.

International audienceMethyliminopropadienone MeN=C=C=C=O 1a was generated by flash vacuum thermolysis from four different precursors and isolated in solid argon. The matrix-isolation IR spectrum is dominated by unusually strong anharmonic effects resulting in complex fine structure of the absorptions due to the NCCCO moiety in the 2200 cm-1 region. Doubling and tripling of the corresponding absorption bands are obsd. for phenyliminopropadienone PhN=C=C=C=O 1b and bis(phenylimino)propadiene PhN=C=C=C=NPh 9, resp. Anharmonic vibrational frequency calcns. allow the identification of a no. of overtones and combination bands as the cause of the splittings for each mol. This method constitutes an important tool for the characterization of reactive intermediates and unusual mols. by matrix-isolation IR spectroscopy