Abundant data have been accumulated to indicate that cyclopropyl group to the carbonium-ion center occurs best not from the parallel one (II).') the electronic contribution of the from the bisected arrangement (I) and II This has been successfully shown by the studies of the rates of solvolysis of III 3) and IV,4) and the pKR+ of the cation derived from V, 5) where the cyclopropyl groups are constrained to such geometries that cannot achieve the bisected arrangement in the stages of carbonium ions. In the above works, however, such conformational effects examined were concerned with those of the cyclopropyl groups either located at a position distant from the carbonium-ion center across the benzene ring in the t-cumyl (III) and the trityl (V) systems, or fixed in the rigid parallel arrangement in the transient cation derived from IV. In the course of our study of one-electron reduction of various substituted tropylium ions, 6) we were interested to see the conformational effects of the cyclopropyl group as a substituent on the stability of the tropylium ion, as estimated from the rates of the one-electron reduction (es. 1), because the tropylium system was thought to be unique in that the electronic contribution of the cyclopropyl group is directly transmitted to the carbonium carbon, and moreover, the conformation is easily controlled by introducing flanking methyl groups to the tropylium ring. 10) Attempts to determine the pKRf's failed for most of VI, VII, and VIII owing to their instability in aqueous ethanol. Therefore, the correlation of log k2 with pKR+ could not be examined. 11) The plot of log k2 for Via-c against the a+-values 14,15) gives a straight line with o+ +2.61 (correlation coefficient 0.9993, standard deviation along tfie ordinate 0.024). Therefore, electronic contribution of the cyclopropyl group in the reaction (eq. 1) is believed to be much greater to the cation than to the produced radical. 12) The log k2 values have been successfully correlated with C. T. energy (vmax) for monosubstituted tropylium ions.6) In the present work, however, di-and tri-substituted tropylium ions showed vmax values (2.10-2.11x10~4cm-1) similar to each other, with pyrene as the standard eTeciron donor. IT-II'S appears to suggest the levering of electron &JocaJizatiw from the aTkyT groups to the fropyrium ring in the C. T. compTex formation, and the research aTong this line is underway. 13) The 'H NMR spectra of VIc, VIIc, and VIIIc also suggest that the delocalization of the pcositive charge to the cycloprop_v> group Becreases jn this order,