The reduction rate of mono-methylated ketone nitroxide 5, however, does not differ significantly from that of the nonmethylated version 10. This is also in agreement with the open conformation adopted in the crystal structure of this compound (Scheme 1B). Surprisingly, the dimethylated ketone 8, which was used as a mixture of diastereomers, is reduced more rapidly than all other spirocyclic nitroxides. While the transdiastereomer of 8 adopts a semi-open conformation in the solid state (Scheme 1B), the preferred conformation of the other diastereomer is unknown. Thus, at this point the conformation of 8 cannot be related to the reactivity.