'H-and "C-NMR spectra of a series of 8-RI-substituted as well as of 8,8-R', Rz-disubstituted heptafulvenes, varying from inversely polarized (31) to unpolar (3h) and polar heptafulvenes with electron-withdrawing groups (3d, e, 0, have been analyzed and compared with those of methoxytropylium salt 5a. The results concerning 3J (H,H) values and '3C-chemical shifts are shown in Figs. 5 and 6. It turns out that all the NMR parameters are strongly influenced by substituents R', R2, but, contrary to planar pentafulvenes, no linear correlations of the NMR parameter us. Hammett substituent constants u+ are obtained in the series 31 + 3d. ' J coupling constants J(2,3)/J(4,5) and J(3,4) are not much influenced by substituent changes in the series 31 + 3h, but are approaching in the row 3h + 3d. Similarly, signals of the I3C-atoms undergo a moderate shift to higher frequencies in the row 31 + 3h but are strongly influenced by -M groups, whereby the sensitivity is decreasing in the series C(7) > C(2)/ C(5) > C(3)/C(4) > C(l)/C(6). These results are essentially explained by a boat conformation of inversely polarized heptafulvenes of the type 31 and an increasing planarization of the ring on going to polar heptafulvenes of type 3d.