Search results for "Nitrogen inversion"
showing 3 items of 3 documents
Structural study of ethyl 3-arylcarbamoyl-2,3-diazabicyclo[2.2.1]hept-5-ene-2-carboxylates: conformation and transmission of substituent effects acro…
2001
Nine new ethyl 3-arylcarbamoyl-2,3-diazabicyclo[2.2.1]hept-5-ene-2-carboxylates were prepared by a [4 + 2] cycloaddition and their FTIR, 1H, 13C and 15N NMR spectra were measured and assigned. Single crystals were grown for five compounds and their X-ray data were obtained. The electronic structure and the conformations were calculated by the semi-empirical AM1 method. Using correlations between the spectral, empirical and theoretical structural data, the transmission of substituent effects and the preferential conformation connected with the consecutive double nitrogen inversion and regarding the mutual orientation of NH and CO bonds were investigated. The results are compared with those f…
The in, out Asymmetric Pseudo-Triple Helical Form of a D3h Diaza-Macropentacycle
2007
A sterically encumbered [N(2)S(6)] macropentacycle (5) related to diazamacrobicycles and cryptands has been synthesized in 53% yield by the [1+1] condensation reaction between functionalized macrocyclic and macrotricyclic precursors. A macrononacycle (18) resulting from the corresponding [2+2] condensation was isolated in 7% yield from the reaction mixture. Both compounds showed broad features in their room-temperature (1)H NMR spectra, but their maximal average symmetry (D(3h) and D(2h), respectively) was achieved at high temperature (380 K). At low temperature (200 K, CD(2)Cl(2) solution), the macropentacycle is "frozen" to a single asymmetric (C1) conformation on the (1)H NMR time scale,…
1988
The structure of 1-azabicyclo[4.2.0]octane (1) was evaluated by NMR spectroscopy. It was found that the six-membered ring has a chair conformation with the four membered ring in the N-axial and C-6-equatorial position, and as a consequence, the monomer allows neither a ring inversion nor a nitrogen inversion. It possesses two centers of chirality, one at the nitrogen atom and one at C-6. Homopolymerization was carried out in methanol at 60°C with N-alkyl ammonium salts of 1 affording the polymer in high yield within a few hours. Its NMR spectra reveal that the polymer chain is preferably arranged in the biequatorial position of the six-membered ring. As a polybase the polymer can be titrate…