Crystallographic analysis. Next, we compared the geometric properties of 2-oxabicyclo[2.2.2]octanes with those of the parasubstituted phenyl ring, and the previously used bioisosteresbicyclo[2.2.2]octanes. For that, we measured two C-C distances r and d to see the overall similarity of cores; and two angles φ1 and φ2 to estimate the collinearity of exit vectors (Figure ).