With the scaffold of interest in hand, our attention turned towards investigating the conformations adopted by the spirocyclohexyl moieties. The direct application of twodimensional NMR spectroscopy to investigate the conformations of nitroxides is prevented by severe signal broadening caused by paramagnetic relaxation enhancement. Although in situ reduction of the nitroxide to a diamagnetic hydroxylamine can enable investigation of these scaffolds by NMR, significant overlap of the resonances of the diagnostic spirocyclic protons makes this approach highly challenging. As reduction to a hydroxylamine leads to a pyramidalization of the otherwise planar nitroxide, this approach can, moreover, alter the conformational distribution of the nitroxides. Instead, we opted for single-crystal X-ray diffraction (SC-XRD) as the optimal method to assess nitroxide conformations. Among the five-membered nitroxides with known X-ray structures, a majority adopt either open or semi-open conformations. Although nitroxide 7 is an oil in neat form, we were able to prepare a metal-organic framework (MOF) inclusion complex of this nitroxide and successfully determine its crystal structure by the crystalline sponge method (Figure ). This structure clearly shows that nitroxide 7 adopts an open conformation (Figure ). We were also able to hydrolyse ester 7 to the carboxylic acid 8 (Scheme 1), which amusingly is a crystalline solid. The solid-state structure of nitroxide 8 was also determined through X-ray crystallography, revealing that the spirocyclohexyl substituents adopt an open conformation in the solid state even outside the microporous MOF environment (Figure ). Although these results suggest that the exo-methylene substituent does not bias nitroxides toward adopting closed conformations, our prior research on substituted nitroxides has revealed that the solid-state structure does not always accurately reflect the behaviour observed in solution. Therefore, it was nevertheless of significant interest to explore the kinetic and thermodynamic stability of exo-methylene nitroxides towards redox reactions.