Taking into account the findings of experiment and computation, we considered a pericyclic syn elimination featuring a 6-membered transition state (Figure ) as a plausible reaction mechanism. Such an Ei mechanism was reported before for the preparative conversion of aldehydes into nitriles using oximes underscoring our hypothesis. Notably, the Ei pathway yielded products identical to the homolytic scission under mechanochemical conditions. Since the carbamoylketoximes were thermally stable and only showed non-specific degradation upon heating at 170 °C, we deemed an investigation of the thermal reaction pathway futile and hence proceeded with comparative photochemical experiments. Carbamoylketoximes are prominent photobase generators to uncage latent amines, yet require the addition of a triplet sensitizer since the photochemical N-O scission occurs from the T1 state. MKO was therefore irradiated at 254 nm for 1 h in the presence of DMPO with and without the addition of the typically used photosensitizer 4methoxyacetophenone (MAP, Figure ). While irradiation of AO with light in the presence of DMPO yielded the expected nitrile without the consumption of the spin trap (Figure ), the depletion of DMPO at 6.80 ppm was observed for the irradiation of MKO (Figure ). This underscored the pericyclic character of the aldoxime photoreaction and the homolytic character of the ketoxime photoreaction. The aromatic protons of MKO showed a small shift after trapping and overlapped with two peaks around 7.4 ppm resulting from incomplete trapping in 1 h in the absence of MAP. MKO photolysis was greatly accelerated by MAP, emphasizing the scission from the T1 state (Figure and S9).