'H-and 13C-NMR spectra of a series of 6-(p-X-phenyl)pentafulvenes 1-9 as well as of 6-R-substituted and 6,6-R',R2-disubstituted pentafulvenes 1&23 have been analysed. It turns out that the n-system of pentafulvenes is an attractive probe for the investigation ofelectronic substituent effects. Changes of uicinal H,H-coupling consfanis with increasing electron-donating capacity of the substituents X and R are interpreted in terms of an increasing x delocalisation in the 5-membered ring, and linear correlations of Hammett substituent constants 0: or MNDO-calculated C-C bond lengths and 3J values are observed. On the other hand, a systematic high-field shift of "C chemical shifis of the ring C-atoms is induced by electron-releasing substituents R and X, which decreases in the series C(5) > C(2)/C(3) > C(I)/C(4), and which mainly reflects changes in n-charge density.
'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.
(1 1.IX.91)A simple criterion for estimating the extent of a delocalization in the five-membered ring of pentafulvenes and pentafulvalenes is described. It is based on the fact that changes of bond lengths (induced by exocyclic substituents R'-R2 of 1) are reflected by systematic changes of 3J(H,H) values, so that linear correlations ofn; us. 3J(H,H) are obtained. Plots of that type (Fig.1) are very useful for determining the extent of a delocalization of various pentafulvalenes 2-5 (Fig. 3 ) which show a very similar behavior to pentafulvenes. In principle, these plots could additionally be used for estimating snbstituent constants u,' or for approximating the extent of z overlap between exocyclic substituents and the 7z system of pentafulvenes. Charge-density effects of pentafulvenes and pentafulvalenes are observed by substituent-induced shifts of the ring C-atoms (Fig.4) Today all the spectroscopic data are in agreement with a basically olefinic character of parent pentafulvene which shows strongly alternating bond lengths, and is best represented by the canonical structure 1A. On the other hand, exocyclic substituents R' and R2 with electron-donating capacity might considerably enhance the importance of dipolar canonical structure lB, thus increasing n -bond delocalization as well as negative ncharge density in the ring. So the investigation of substituent effects on n delocalization of pentafulvenes is very attractive. Fortunately, contrary to heptafulvenes [I] and nonaful-
Herrn Prof. Dr. Huns Nitschmann zum 80. Ceburtstag gewidnict (25.11.87) Synthesis and NMR Spectra of Nonafulvene and Comparison with 10-PhenylnonafulveneExperimental procedures for the reaction of cis,cis,ci.s,trans-cyclononatetraenide (ccct -CNT-; see 4) with bromomethyl acetate (la, R = H, X = Br) to give (cyclononatetraeny1)methyl acetate (Sa; 84% yield) as well as for the base-induced elimination of HOAc from 5a to give nonafulvene (6a; 44% yield) are described. Spectroscopic as well as chemical evidence for 6a and 6b is presented. An approximate high-field-NMR analysis of 6a and 6b has been completed. The results are in favour of a fast interconversion of the type 6A*6B /Scheme 4 ) . and supported by the MNDO-optimised geometry of 6a. The first X-ray analysis of a cyclononatetraene (i.e. of Sb) has been accomplished: 5b is a polyolefinic molecule with largely alternating bond lengths and with a nine-membered ring deviating strongly from planarity.1. Einleitung. -Essigsaure-(a-halogenalky1)ester 1 sind aus aliphatischen und aromatischen Aldehyden sowie Acetyl-chlorid oder Acetyl-bromid bei Katalyse mit Lewis-Sburen in einer einfachen Eintopfreaktion zuganglich [5]. Unter optimalen Reaktionsbedingungen lassen sich Nebenprodukte weitgehend vermeiden [6] und oft fast quantitative Ausbeuten erzielen [513). Die bifunktionellen Carbonyl-Derivate besitzen zwei Abgangsgruppen unterschiedlicher nucleofuger Eigenschaften und gehen naturgemass im basischen Milieu keine Nebenreaktionen des Aldol-Typs ein. Wir haben diese Vorteile bei der Entwicklung einer allgemeinen Pentafulven-Synthese ausgenutzt (Schema 1 ) und ge-
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