13 C NMR and lanthanide‐induced shifts in epoxides of Terpenes and related compounds

Based on literature data, and new measurements with both simple and complicated skeletons, it is shown that epoxidation‐induced shifts (EIS) usually vary by only <4ppm if compared with the corresponding olefins, but by <9 ppm if compared with the saturated analogues. Shift differences between stereoisomers (E/Z or trans/cis ) are consistent and, again, similar in epoxides and olefins. Larger variations are observed only for cyclic systems in which flexibility and conformational coupling can lead to significant conformational differences between the epoxide and olefin. Yb(fod) 3 ‐induced LIS values are regular if normalized by setting the LIS for the α‐carbon atoms to 100%; these and the EIS values can be used to confirm or correct 13 C signal assignments.