IR-spectroscopic investigations of light-induced rearrangement reactions of nitrosooxymethane (CH,ONO), nitrosooxyethane (CH,CH,ONO) and N,N-dimethylnitrosamine ((CH,),NNO) in low-temperature rare-gas matrices have established that these molecules are transformed in two photolysis steps to the previously unknown C-nitroso compounds nitrosomethanol (CH,(OH)(NO)), 1-nitrosoethanol (CH,CH(OH)(NO)), and methyl(nitrosomethy1)amine (CH,(NO)(NH)CH,). Evidence for a similar rearrangement reaction has been advanced for N-nitrosopyrrolidine (k,H,kNO) which is converted to C-nitrosopyrrolidine (k,H,CH(NO)(&H)). The matrix-isolation technique in combination with wavelength-selective irradiation allowed to trap and characterize an intermediate of the rearrangement which revealed to be a nitroxyl (HNO) complex (CH,O.. . HNO, CH,CHO.. .HNO, -CH,N = CH, ... HNO, and e,H,CH = $I... HNO). Since these findings have a close resemblance with rearrangement reactions of more complex nitrosooxy compounds, nitrosamines, or nitrosohydrazines used in organic synthesis, it is suggested that also in these reactions nitroxyl is present as an intermediate species.