In conclusion, we have developed a synthetic route to new spirocyclic nitroxide pyrrolidine scaffolds with an exocyclic methylene substituent. Surprisingly, this additional substituent does not appear to significantly influence the conformations adopted by the scaffold, as indicated by X-ray crystallography. Kinetic decay measurements with EPR monitoring show that the presence of the exo-methylene substituent does not lead to increased stability of the nitroxide under reducing conditions. A carboxylate functionality, however, is found to have a considerable stabilizing effect, even when located at a remote position in the scaffold. Circular voltammetry measurements indicate that the thermodynamic redox window of nitroxides based on the new exo-methylene scaffold is slightly narrower than nitroxides from the more established pyrroline family. The electron spin relaxation properties of the new nitroxides, meanwhile, are unaffected by the additional exo-methylene group, with excellent phase coherence times (Tm) maintained until 160 K as measured by pulsed EPR methods.