Carbethoxynitrene, EtOOCN, can be generated by CY-elimination from the anion of Np- nitrobenzenesuvonoxyurethan (I). The product mixtures produced with isopentane, cyclohexane, cyclohexene, and benzene are the same as those produced by photolytic decomposition of ethyI azidoformate in these substrates. Insensitivity toward dilution shows that the reactive intermediate is not in a vibrationally excited state.