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- W1983669917 abstract "Das Titelsystem (I/II) konnte durch regiospezifische Alkylierung am Carbonylsauerstoffatom von N-Acylimidsäureestern 4 mit Trialkyloxonium-Salzen präparativ zugänglich gemacht werden. Die Salze 3 liegen im Kristall nach einer Röntgenstrukturbestimmung (3a) als Kompromißform aus beiden Strukturtypen I und II vor, wobei die Alkoxysubstituenten exo in s-cis-Konformation stehen (C N C-Winkel 133.0°, Torsionswinkel 70.4°). Quantenmechanische Berechnungen (3-21G-ab initio) sagen für die Stammverbindung, die N-Formylformimidsäure 6a, eine bevorzugte Protonierung am Stickstoffatom zum Ion 7a voraus, eine Sauerstoffprotonierung zur allenartigen Struktur 8a soll um 11.4 kcal/mol ungünstiger sein. Allen- (8a) und Allyl-Form (9a) sind nur um ca. 5 kcal/mol verschieden und sollten daher extrem leicht ineinander übergehen. 1H-NMR-Spektren bestätigen das Vorliegen chiraler, allenartiger Strukturen 3a bei tiefer Temperatur, bei erhöhter Temperatur tritt rasche Äquilibrierung ein. Structural Study of the System 1,3-Dialkoxy-2-aza-allenium Ions/1,3-Dialkoxy-2-aza-allyl Cations The title system (I/II) is experimentally accessible by regiospecific alkylation at the carbonyl oxygen of alkyl N-acylimidates 4 using trialkyloxonium salts. According to an X-ray investigation (3a), the salts 3 form a compromise structure between both isomeric forms, the alkoxy substituents being in exo positions in s-cis-conformations (C N C-bond angle 133.0°, torsional angle 70.4°). Quantum mechanical calculations (3-21G ab initio) for the parent substance N-formylformimidic acid 6a predict preferred nitrogen protonation giving 7a. Oxygen protonation leading to the allenic structure 8a is disfavoured by 11.4 kcal/mol. The allenic- (8a) and the allyl structure (9a) differ by only ca. 5 kcal/mol and indicate therefore enormous structural flexibility of the title system. 1H NMR spectra support the existence of chiral isomers of 3a at low temperatures; at higher temperatures rapid equilibration takes place." @default.
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- W1983669917 date "1985-09-01" @default.
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- W1983669917 title "Strukturuntersuchungen zum System 1,3‐Dialkoxy‐2‐aza‐allenium‐Ionen/1,3‐Dialkoxy‐2‐aza‐allyl‐Kationen" @default.
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- W1983669917 doi "https://doi.org/10.1002/cber.19851180917" @default.
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