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Nitrogen Inversion (nitrogen + inversion)
Selected AbstractsStructural study of ethyl 3-arylcarbamoyl-2,3-diazabicyclo[2.2.1]hept-5-ene-2-carboxylates: conformation and transmission of substituent effects across the diazabicycloheptene ring,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 11 2001A. Perjéssy Abstract 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 for a previously reported series of analogous ethyl 2-arylcarbamoyl-4,5-dimethyl-1,2,3,6-tetrahydropyridazine-1-carboxylates. Copyright © 2001 John Wiley & Sons, Ltd. [source] NMR study of quinolizidine alkaloids: relative configurations, conformations,MAGNETIC RESONANCE IN CHEMISTRY, Issue 4 2005Phuong Mai Le Abstract Extracts of fruits and leaves of Connarus paniculatus afford six quinolizidine alkaloids which were identified as piptanthine, 18-epipiptanthine, ormosanine, homoormosanine, podopetaline (monohydrochloride) and homopodopetaline on the basis of high-field NMR studies. 1D and 2D NMR experiments provide complete assignments of the 1H and 13C spectra. In conjunction with detection of nuclear Overhauser effects (NOESY), these results allow detailed structure characterization including determination of relative configurations for the chiral sites and conformational analysis. Exchange phenomena involving nitrogen inversion were detected. Copyright © 2005 John Wiley & Sons, Ltd. [source] 1H,NMR Spectroscopic Studies of the Conformational Isomers of PyrrolidinofullerenesCHEMISTRY - A EUROPEAN JOURNAL, Issue 29 2007Olena Lukoyanova Abstract Mixed bis-adduct derivatives of C60 containing a pyrrolidine and a malonate methano group were synthesized. Three regioisomers, the e,, the trans -2, and the trans -3, were isolated and characterized. In-depth NMR studies of these methano-pyrrolidinofullerenes showed that the nitrogen inversion on the pyrrolidine moiety is not a fast event in the 1H,NMR time scale as previously regarded. Solvent effects, variable temperature experiments, and protonation of the pyrrolidine nitrogen are addressed. [source] Trianglamines,Readily Prepared, Conformationally Flexible Inclusion-Forming Chiral HexaminesCHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2006Jacek Gawronski Prof. Dr. Abstract Trianglamines, macrocyclic heteraphanes, were readily synthesised through a [3+3] cyclocondensation of (R,R)-1,2-diaminocyclohexane with terephthalaldehyde, followed by NaBH4 reduction and N-alkylation. The macrocyclic ring shows a remarkable ability to change its conformation, as a consequence of rotation about the CN bonds or nitrogen inversion due to protonation or N-alkylation, as revealed by circular dichroism spectra, computational modelling and X-ray diffraction analysis. The flexible natures of the trianglamine macrocycles allow ready accommodation of a variety of guest molecules to form crystalline inclusion complexes of highly diversified interpenetrating structures. [source] The stereodynamics of 1,2-dipropyldiaziridinesCHIRALITY, Issue 2 2010Oliver Trapp Abstract N-alkylated trans -diaziridines are an intriguing class of compounds with two stereogenic nitrogen atoms which easily interconvert. In the course of our investigations of the nature of the interconversion process via nitrogen inversion or electrocyclic ring opening ring closure, we synthesized and characterized the three constitutionally isomeric diaziridines 1,2-di- n -propyldiaziridine 1, 1-isopropyl-2- n -propyldiaziridine 2, and 1,2-diisopropyldiaziridine 3 to study the influence of the substituents on the interconversion barriers. Enantiomer separation was achieved by enantioselective gas chromatography on the chiral stationary phase Chirasil-,-Dex with high separation factors , (1-isopropyl-2- n -propyldiaziridine: 1.18; 1, 2-diisopropyldiaziridine: 1.24; 100°C 50 kPa He) for the isopropyl substituted diaziridines. These compounds showed pronounced plateau formation between 100 and 150°C, and peak coalescence at elevated temperatures. The enantiomerization barriers ,G, and activation parameters ,H, and ,S, were determined by enantioselective dynamic gas chromatography (DGC) and direct evaluation of the elution profiles using the unified equation implemented in the software DCXplorer. Interestingly, 1-isopropyl-2- n -propyldiaziridine and 1,2-diisopropyldiaziridine exhibit similar high interconversion barriers ,G, (100°C) of 128.3 ± 0.4 kJ mol,1 and 129.8 ± 0.4 kJ mol,1, respectively, which indicates that two sterically demanding substituents do not substantially increase the barrier as expected for a distinct nitrogen inversion process. Chirality, 2010. © 2009 Wiley-Liss, Inc. [source] | ||||||||||