A computational analysis using density functional theory (DFT, PBE0-D3BJ/def2-TZVPP[IEFPCM]) was performed to assess the impact of additional nitroxide ring substitution across the conformational equilibrium. To this end, Gibbs free energies and Boltzmann distributions were computed for open, semiopen and closed conformations of nitroxides 9 and 11 (Figure ). which can exist as the diastereomers cis,cis-9, trans,trans-9 and cis,trans-9 (Figure ). For cis,cis-9 there are two low-energy conformations: a closed structure with equatorial methyl groups (as also observed in the solid-state crystal structure, Scheme 1), and an open conformation with both methyls in axial positions (Figure ). Assuming rapid conformational interconversion, these two conformers dominate in solution, in an approximate ratio of 1:2. This supports our hypothesis that methyl substituents at the 3-and 5-positions of the nitroxide ring exert a steric pressure that can result in a closed conformation. The computations show that the relative stereochemical configurations of the hydroxyl group and the substituted 3-and 5-positions of 9 are important. Whereas the diastereomer trans,trans-9 displays a significant preference for the closed over the open conformation by 2.7 kcal/mol (Figure ), the third possible diastereomer, cis,trans-9, prefers a semiopen conformation, with the favoured structure displaying a trans-relationship between the hydroxyl and methyl group close to the closed spirocyclohexyl. Our results indicate that only methyl substituents in an equatorial position on the central nitroxide ring are able to maximise the steric pressure and enforce a closed conformation of the nearby spirocyclohexyl rings.