Neue Heptafulven‐Derivate

'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.

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“…[23], cycloheptatriene 6a [46], and tropylium ion 5a [47] have been prepared according to literature procedures.…”

Section: Experimental Partmentioning

confidence: 99%

¹H‐ and ¹³C‐NMR Investigations of Heptafulvenes

Bönzli

Neuenschwander

1991

Helvetica Chimica Acta

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“…Chem. (16) Anderson and Fife actually followed kinetics using a wavelength of 31 1 nm. (14) T. H. Fife and E. Anderson, J. Org.…”

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confidence: 99%

The reactivity of oxocarbonium ions. 2. Hydrolysis in sulfuric acid solutions and estimates of reactivity in water

McClelland¹,

Ahmad²

1978

J. Am. Chem. Soc.

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McClelland, Ahmad 1 Oxocarbonium Ion Hydrolysis in Sulfuric Acid Solutions 703 1Kinetic and spectral investigations were carried out using a Unicam SP 1800 spectrometer with cell block thermostated at 25.0 f 0.1 OC or a Durrum-Gibson stopped-flow spectrophotometer, also operating at 25.0 f 0.1 "C. The dead time of the latter was determined using a published procedure.26 First-order rate constants were obtained from plots of In ( A , -A m ) or In ( A , -A , ) vs. time.Acknowledgment. Financial support from the National Research Council of Canada is gratefully acknowledged.

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“…2) of (7) in CH3CN exhibits a maximum at 450nm however, when one drop of HBF4 was added to the solution, the curve exhibits two maxima at 443 nm and 610 (3.58), and is a similar to that of trimethine ditropylium cation (10) reported by Hafner et al 4 Therefore, it is clear that the compound (7) easily undergoes a protonation at the carbonyl oxygen to form a hydroxy monocation (11). However, it is found that the compound (7) changes to dication (6) (X-=CF3COO-) in trifluoroacetic acid solution, because of the color of the solution is reddish and the nmr of (7) in trifluoroacetic acid is almost the same with that of (6) (X-=BF 4-) in the same solvent.5…”

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confidence: 52%