SPECTROSCOPY OF ACYL AND CARBONYL ISOCYANATES

The gas phase IR, gas phase UV and solution C-13 NMR spectroscopic dat a for seven carbonyl isocyanates X-CO-NCO and eight acyl isocyanates R -CO-NCO are reported. The IR group frequencies are assigned and substi tuent-frequency relationships are given for the C=O and NCO stretching frequencies. For carbonyl isocyanates the IR spectra show features of isomeric nonuniformity which are interpreted in terms of cisoid and t ransoid conformations. For all acyl isocyanates the IR spectra suggest the presence of the cisoid conformation only. pi --> pi and n --> pi transitions are assigned for the gas phase UV spectra and the C-13 c hemical shifts for the carbonyl and isocyanato carbons are reported. G eneralized spectroscopic data, together with theoretical data, indicat e a small degree of resonance interaction between the carbonyl and iso cyanato groups.