C-nitroso compounds—XXIV: Photolysis of some geminal nitro-nitrosoalkanes (“pseudonitroles”)

Photolysis of the “pseudonitrole” 1-nitro-1-nitrosocyclohexane with red light in the absence of oxygen occurs by homolytic C-NO fission, and generates a radical pair: NO and the α-nitro-cyclohexyl radical. If one radical of this pair adds to the NO-group of unchanged starting material, there results a paramagnetic nitroxide, that can combine with the other radical of the pair to a diamagnetic intermediate, forming two isomeric intermediate adducts to the NO double bond. The ratio in which these isomers are formed depends on solvent. In methanol, solvolysis leads to equimolar amounts of cyclohexanone and cyclohexanone-oxime, together with methyl nitrite. In benzene, the major product is cyclohexanone. Small amounts are formed of 1,1-dinitrocyclohexane, 1-nitrocyclohexene and nitrocyclohexane; arising directly from the α-nitrocyclohexyl radical. The nitroxide derived from this radical and the starting material can be detected by ESR.The photolytic behaviour of 1-nitro-1-nitroso-1-cyclopropylethane illustrates the strong interaction between a nitrogroup and an adjacent C-radical centre: only ring-closed products are formed, showing considerable spin delocalisation away from the cyclopropyl ring.