1 H and 13 C NMR study of the effects exerted by an oxirane ring in the epoxybicyclo‐[2.2.2]octane series

The 1 H and 13 C NMR spectra of 2,3‐disubstituted exo ‐5,6‐ and endo ‐5,6‐bicyclo[2.2.2]octanes, and the corresponding alkanes, have been investigated to determine the effects exerted by an oxirane ring. The 1 H NMR study showed that the anti protons, H‐7 a and H‐8 a , are significantly shielded and the syn protons, H‐7 s and H‐8 s , are deshielded, although to a smaller extent, by the exo ‐oxirane. An endo ‐oxirane has practically no effect on the same protons. The stereochemistry of epoxybicyclo[2.2.2]octanes is, thus, easily deduced from 1 H NMR data. The 13 C NMR study of the epoxy compounds provided an estimate of the value of α, β, γ syn and γ anti effects (to the epoxide oxygen) of an oxirane ring. In these rigid bicyclic molecules, of known geometry, the γ syn and the γ anti effects are of the same value, even though the dihedral angles are very different (0° and 120°).