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In numerous organometallic complexes n-electrons are highly or even completely delocalized. In many cases chemical methods do not distinguish between a rapid equilibrium Involving two asymmetric structures or a single symmetrie structure. This problem can be solved by vibrational spectroscopy of isotopically labeled molecules. In metal acetylacetonates delocalisation between single and double bonds is complete. Nuclear magnctic resonance spectra of properly substituted derivatives unambigously show that these chelate rings have no aromatic character in contrast to arguments based on their…mehr

Produktbeschreibung
In numerous organometallic complexes n-electrons are highly or even completely delocalized. In many cases chemical methods do not distinguish between a rapid equilibrium Involving two asymmetric structures or a single symmetrie structure. This problem can be solved by vibrational spectroscopy of isotopically labeled molecules. In metal acetylacetonates delocalisation between single and double bonds is complete. Nuclear magnctic resonance spectra of properly substituted derivatives unambigously show that these chelate rings have no aromatic character in contrast to arguments based on their chemical properties. Resume En beaucoup de composes organometalliques les electrons des double liaisons sont vastement ou totalement delocalises. Frequemment il est impossible de decider avec les methodes chimiques d'un rapide equilibre entre deux structures asymetriques ou une seule structure symetrique. On peut resoudre ce probleme a l'aide des spectres infrarouges des mole cules marquees avec
des isotopes. En les complexes metalliques d'acetylacetone la delocalisation entre les simple et les double liaisons est complete. Quoique le comportement chimique de ces composes indique un " caractere aromatique", les spectres RMN des composes substitues proprement montrent que ces chelates ne sont pas aromatiques. Diskussion Professor Dr. rer. nato Burchard Franck : Ich habe zunächst eine Frage zur Kernresonanz-Methode. \'V'enn die Aktivierungsenergie der Protonenver schiebung auch kleiner als 10 kcaljMol ist, so könnte es doch vielleich mög lich sein, durch Kernresonanzmessung bei tiefer Temperatur eine Aussage über den aromatischen Charakter der Komplexe zu erhalten.
Autorenporträt
Prof. Dr. Harald Schäfer ist Steuerberater und Wirtschaftsprüfer in Mannheim.