Alkylvinyl nitroxides with considerable delocalisation of the unpaired electron into the vinyl group are obtained for the first time by spin trapping using the unusually stable nitrosoalkene 1. Increase of the coupling constants of the protons at Cα with increasing steric hindrance in the radicals is explained by hyperconjugation in twisted π-radicals. The phenyl vinyl nitroxide 2e is shown to be twisted to about 50° at the N Cα-bond. Radical ...