Abstract: Carbonium ion reactivities of sixteen bridgehead systems which vary by more than eighteen powers of ten are correlated by quantitative conformational analysis. Bicyclic substrates ranging from l-bicyclo [2.2. l] heptyl to l-bicycl0 [3.3. 2] decyl and a wide variety of tricyclic and fused ring systems (Figure 1) are treated. Since correlation between the available bridgehead radical and carbonium ion reactivities is observed, the same ...