The effects of slight changes in structure on reactivity was tested by comparing rates of ring closures of identical rings attached to bicyclo-[2,2,1] and -[2,2,2] supporting ring structures; the rates of the γ-lactonizations and γ-thiolactonizations were found to be 21 and 52 fold greater for the bicyclo[2,2,2] compounds compared to their bicyclo[2,2,1] analogues.