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1 H‐ and 13 C‐NMR Investigations of Heptafulvenes
Author(s) -
Bönzli Peter,
Neuenschwander Markus
Publication year - 1991
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19910740203
Subject(s) - chemistry , substituent , chemical shift , coupling constant , nmr spectra database , crystallography , spectral line , polar , stereochemistry , ring (chemistry) , organic chemistry , physics , particle physics , astronomy
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 .