Die Wechselwirkung zwischen Walsh- und π-Orbitalen im 7-Cyclopropyliden-norbornadien

The qualitative analysis of the PE.-spectrum of 7-cyclopropylidene-norbornadiene ( 3 ) shows that the ‘through-space’ interaction of the e _A-Walsh orbital with the antisymmetric linear combination \documentclass{article}\pagestyle{empty}\begin{document}$ {{\pi _ - = (\pi _a - \pi _b)} \mathord{\left/ {\vphantom {{\pi _ - = (\pi _a - \pi _b)} {\sqrt 2}}} \right. \kern-\nulldelimiterspace} {\sqrt 2}} $\end{document} of the two π-orbitals in 3 is of the same order as the analogous interaction between π- and the π-orbital of the exocyclic double bond in 7-isopropylidene-norbornadiene ( 2 ).     

Nachweis von π → σ-Umlagerungen bei Ligandenverdrängungsreaktionen von π-Allyl-π-cyclopentadienyl-Palladiumkomplexen

It has been proved by NMR. measurements at low temperatures that the ligand displacement reactions of (π-all)Pd(π-C₅H₅) and Lewis bases L yielding PdL₄ proceed by a π → σ rearrangement of the allylic group as the primary step. The organic reaction product is the 1-isomer of the corresponding allylcyclopentadiene but in the reactions of (π-1,1,2-Me₃C₃H₂)Pd(π-C₅H₅) with L besides the isomeric allylcyclopentadienes also 2,3-dimethylbutadiene and cyclopentadiene are formed. The reaction mechanism will be discussed.     

σ, π-Isomerisierungen von Monohetero-σ-bishomobenzol-Derivaten. Vorläufige Mitteilung

The cis-oxa- ( 13a-d ) and -aza-σ-bishomobenzene ( 13 e ) derivatives have been synthesized; they are sufficiently stable to be isolated in pure form. On heating, 13a-e are easily isomerized into the π-bishomobenzene analogues 14a-e , the processes 13 a ? 14 a , 13 b ? 14b and 13d ? 14d being reversible. Some kinetic and thermodynamic data for these σ, π,bishomobenzene transformations are presented.