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Die Zusammenhlnge zwischen NMR-Spektren und Stereochemie von Bicyclo-[2.2.2]octan-Derivaten wurden untersucht. Eine Doppelbindung oder ein ankondensierter Benzolring verursachen im Bicyclooctan und seinem Benzoderivat cine diamagnetixhe Abschirrnung der Ringprotonen bzw. der H-Atorne von Substituenten an anderen Brucken, wodurch deren Absorptionssignale nach niedrigeren oder hbheren Feldstarken verschoben werden, je nachdem, ob die Protonen sich in em-oder endo-Stellung zur n-Bindung befinden. Die aus theoretischen u berlegungen erhaltenen Zusatzverschiebungen stimmen mit den experimentellen Werten fast iiberein. Die Einfuhrung einer x-Bindung ermaglicht somit die Festlegung der Konliguration von Substituenten dieses Ringystems aus den Werten der hervorgerufenen Verschiebung der Protonensignale. Im Bicyclooctanring wurden verschiedene ,,long range"-Spinkopplungen nachgewiesen.Jiingste Untersuchungen an N MR-Spektren verbriickter Ringsysteme ergaben einen Zusammenhang zwischen den Spinkopplungskonstanten der Ringprotonen und der Stereochemie der betreffenden Ringsysteme 2-11). Dariiber hinaus wurden verschiedene Arten von ,,long range"-Spinkopplungen aufgefunden 1.3.59-13). Die Konfiguration von Substituenten am verbriickten Ring lieB sich durch Abschatzen der Grok des diamagnetischen Abschirmungseffektes einer Doppelbindung oder eines ankondensierten 1) 11. 26) Der Einfachheit halber wurde die Bezifferung des Bicyclo(2.2.2)octan-Rings sowie die Kenmichnung der Stellung der Protonen und Substituenten an der Briicke in der in Tab. 1 angegebenen Weise vorgenornmen: n, x = eado, ex0 (in Bezug auf die Doppelbindung), s, a = syn, onri (in Bezug auf den Benzolring). Chcmischc Berichte Jabrg. 97 181 Chemistry, S. 129, Pergamon Press, New York 1961.

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Proton magnetic resonance spectra of some norbornane derivatives having double bonds and (or) a benzene ring in the skeleton were studied. Differences in the chemical shifts between the bridge methylenes of norbornene and benzonorbornene and that of norbornane result from the diamagnetic anisotropy effect of a double bond or a benzene ring being in good agreement with the values calculated theoretically. However, in the norbornadiene derivatives which have two double bonds or one olefinic double bond with a benzene ring in a part of the skeleton, the signals of their bridge methylenes show extraordinarily larger downfield shifts by about 0.8 p.p.m. than those expected from the additive shielding due t o each T-electron system. This anomaly is not observed in bicyclo[2.2.2]octane ring series. A large transannular interaction between two a-electron systems in that system would be a major contribution to the above anomaly. , I N T R O D U C T I O SI11 the past few years a number of proton magnetic resonance (n.1n.r.) spectra of bridged ring systems have been investigated, reporting the relations between the spin coupling constants of ring protons and the stereochemistry (1-lo), various types.of long-range spill couplings (3, 5 , 6, 8-11), the establishment of the configuration of substituents by the evaluation of diamagnetic shielding effects of a double bond or a benzene ring (9, 12-15), and so forth (16)(17)(18)(19). However, the substantial features of n.m.r. spsctra of bicyclo[2.2.l]heptane derivatives have not received much attention. By the studies of various ~nonohydroxyl derivatives of bicyclo[2.2.l]heptane1 RIusher (8) has recently reported that (i) a striliitlgly large difference in the magnetic shielding between an exo and an endo proton was obserr~ed, showing larger deshielding on the exo proton, and this difference can not be explained only by the diamagnetic anisotropy of the C-C bonds in the ring; that (ii) the coupling constants between each pair of adjacent protons, JHx-Hx and JIIn-H,*, are not equal; and that (iii) fairly large long-range spin coupling constants were found. On the basis of these results, he suggested the presence of some n-characters in this ring system. I11 a previous paper (20), we also suggested the presence of this character on the basis of the increased s-character of the C-H bonds, which was reflected in the strikingly large values of carbon-hydrogen spin coupling constants J G~~-H obtained from the C13-satellites (21)