1 H‐ and 13 C‐NMR Investigations of Heptafulvenes

1 H‐ and 13 C‐NMR spectra of a series of 8‐R 1 ‐substituted as well as of 8,8‐R 1 , R 2 ‐disubstituted heptafulvenes, varying from inversely polarized ( 3l ) to unpolar ( 3h ) and polar heptafulvenes with electron‐withdrawing groups ( 3d , e , f ), have been analyzed and compared with those of methoxytropylium salt 5a . The results concerning 3 J (H,H) values and 13 C‐chemical shifts are shown in Figs. 5 and 6 . It turns out that all the NMR parameters are strongly influenced by substituents R 1 , R 2 , but contrary to planar pentafulvenes, no linear correlations of the NMR parameter vs. Hammett substituent constant σ + are obtained in the series 3l → 3d . 3 J coupling constants J (2,3)/ J (4,5) and J (3,4) are not much influenced by substituent changes in the series 3l → 3h , but are approaching in the row 3h → 3d . Similarly, signals of the 13 C‐atoms undergo a moderate shift to higher frequencies in the row 3l → 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(1)/C(6). These results are essentially explained by a boat conformation of inversely polarized heptafulvenes of the type 3l and an increasing planarization of the ring on going to polar heptafulvenes of type 3d .