Direct observation of methoxycarbonylnitrene.

The simplest alkoxycarbonylnitrene, CH3 OC(O)N, has been generated through laser (266 and 193 nm) photolysis of CH3 OC(O)N3 and CH3 OC(O)NCO and subsequently characterized by IR (15 N, D-labelling) and EPR (|D/hc| = 1.66 cm-1 and |E/hc| = 0.020 cm-1 ) spectroscopy in cryogenic matrices. Two conformers of the nitrene, with the CH3 group being in syn or anti configuration to the C[double bond, length as m-dash]O bond, have been unambiguously identified. Further UV light irradiation (365 nm) of the nitrene results in isomerization to CH3 ONCO, completing the frequently explored mechanism for the Curtius-rearrangement of CH3 OC(O)N3 .