$^{13}$C NMR Study of the Application of the 'Tool of Increasing Electron Demand' to the 9-Aryl-tricyclo[3.3.1.0$^{2,8}$]non-9-yl, and 8-Aryl-Tetracyclo[3.2.1.0$^{2,7}$.0$^{4,6}$]oct-8-yl cations

$^{13}$C NMR Study of the Application of the 'Tool of Increasing Electron Demand' to the 9-Aryl-tricyclo[3.3.1.0$^{2,8}$]non-9-yl, and 8-Aryl-Tetracyclo[3.2.1.0$^{2,7}$.0$^{4,6}$]oct-8-yl cations

The$^{13}C$ NMR shifts of a series of para-substituted 9-aryl-tricyclo$[3.3.1.0^{2,8}]$non-9-yl and 8-aryl-tetracyclo$[3.2.1.0^{2,7}.0^{4,6}]$-oct-8-yl cations were measured in $FSO_3H/SO_2ClF \;at\; -90^{\circ}C\; or\; -70^{\circ}C$ in order to examine whether the ${\rho}^{c+}$ values can be used to explain the mechanism for the stabilization of the geometrically rigid cyclopropylcarbinyl cations. Plots of the ${\Delta}{\delta}^{c+}$ shifts against ${\sigma}^{c+}$ reveal excellent linear correlation. The tricyclononyl systems yield a ${\rho}^{c+}$ value of -4.95 with a correlation coefficient r = 0.9948. The tetracyclo-octanyl systems give a ${\rho}^{c+}$ value of -6.39 with r = 0.9943. A fair parallelism exists between the results of $^{19}F$ nmr studies and the change of ${\rho}^{c+}$ values in these cations. Accordingly, the present study established that the ${\rho}^{c+}$ value can be used as a mearsure of the geometric influence for the charge delocalization in cyclopropylcarbinyl cations.