The Experts below are selected from a list of 246 Experts worldwide ranked by ideXlab platform
Antonin Lycka - One of the best experts on this subject based on the ideXlab platform.
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15N NMR Spectroscopy in Structural Analysis: An Update(2001-2005)
Current Organic Chemistry, 2007Co-Authors: Radek Marek, Antonin Lycka, Erkki Kolehmainen, Elina Sievänen, Jaromír ToušekAbstract:Since our previous review article (Curr. Org. Chem. 2002, 6, 35), significant improvements and an array of 15N NMR applications in structural analysis have been published. This report aims to update coverage of improvements in methodology and various types of applications published over the period 2001 - 2005. Substantial progress in cryogenic probe technology and the commercial availability of cryoprobes have facilitated the measurement of 15N NMR parameters. The number of solid-state applications has increased significantly during the past few years. In contrast to our previous review, this article covers 15N solid-state studies. The 15N NMR chemical shifts of organic molecules are routinely measured by using cross-polarization magic-angle spinning (CP/MAS) techniques. The principal values of the chemical shift tensors can also be determined. 1H-15N and 2H-15N distance measurements made by means of 1H detection are currently used in NMR crystallography. User friendly quantum chemical programs allow for the routine calculation of 15N chemical shielding and indirect spin-spin coupling constants, especially using density functional theory (DFT). Applications of 15N NMR Spectroscopy in various fields of chemistry are summarized here. Major sections represent tautomerism, complexation, protonation, and hydrogen bonding. The other topics comprise N-alkylation, N-oxidation, regioisomerism, and changes in configuration or conformation.
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15N NMR Spectroscopy in Structural Analysis
Current Organic Chemistry, 2002Co-Authors: Radek Marek, Antonin LyckaAbstract:The implementation of both the directly and the inversely detected 15N NMR techniques at the natural abundance level of the 15N isotope is demonstrated for a diverse array of structural problems in organic chemistry. Following the application of 15N NMR to the elucidation of the structures of natural compounds and synthetic products, the 15N-detected electron distribution in such molecules and following their reactions with other molecules and ions is discussed. A significant part of the 15N structural analysis is devoted to the description of tautomers, rotamers, conformers, configurational isomers, and regioisomers. The changes in the 15N parameters induced in structurally related compounds are described briefly. At present, the optimum probe-tube-sample configuration makes it possible to acquire inverse-detected 1H-15N correlation spectra on samples, where the total available sample is limited to amounts of < 1 mg (for molecules [sim] 400 MHz). 15N NMR Spectroscopy at the natural abundance level of 15N nuclei has become a powerful tool which has substantially extended the analytical arsenal of organic chemists.
Heike Knicker - One of the best experts on this subject based on the ideXlab platform.
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characterization of 15N tnt residues after an anaerobic aerobic treatment of soil molasses mixtures by solid state 15N NMR Spectroscopy 2 systematic investigation of whole soil and different humic fractions
Environmental Science & Technology, 2000Co-Authors: D Brunsnagel, Heike Knicker, Oliver Drzyzga, Klaus Steinbach, Ulf Bütehorn, Diethard Gemsa, Eberhard Von LöwAbstract:An anaerobic/aerobic composting experiment with 15N-2,4,6-trinitrotoluene (TNT) spiked soil was performed to investigate the fate of the explosive under the applied conditions. For a qualitative description of TNT-residues formed during the composting process, bulk soil and different soil fractions were subjected to solid-state 15N NMR Spectroscopy. Major resonance signals could be detected in the chemical shift regions of five-ring heterocyclic nitrogen and in the area of aniline derivatives and primary amines. Distinct nitro peaks were found in the bulk samples and in the humic fractions obtained with a mild extraction procedure. This signal disappeared in the material extracted with a more drastic procedure. Quantitative investigations of the 15N distribution in the composted material revealed that 33% of the stable nitrogen isotope was incorporated into the humic- and fulvic acid, and 23% was present in the humin. Furthermore 38.8% of the 15N present in the composted material could be allotted to cond...
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Characterization of 15N-TNT residues after an anaerobic/aerobic treatment of soil/molasses mixtures by solid-state 15N NMR Spectroscopy. 2. Systematic investigation of whole soil and different humic fractions
Environmental Science & Technology, 2000Co-Authors: D. Bruns-nagel, Heike Knicker, Oliver Drzyzga, Klaus Steinbach, Ulf Bütehorn, Diethard Gemsa, Eberhard Von LöwAbstract:An anaerobic/aerobic composting experiment with 15N-2,4,6-trinitrotoluene (TNT) spiked soil was performed to investigate the fate of the explosive under the applied conditions. For a qualitative description of TNT-residues formed during the composting process, bulk soil and different soil fractions were subjected to solid-state 15N NMR Spectroscopy. Major resonance signals could be detected in the chemical shift regions of five-ring heterocyclic nitrogen and in the area of aniline derivatives and primary amines. Distinct nitro peaks were found in the bulk samples and in the humic fractions obtained with a mild extraction procedure. This signal disappeared in the material extracted with a more drastic procedure. Quantitative investigations of the 15N distribution in the composted material revealed that 33% of the stable nitrogen isotope was incorporated into the humic- and fulvic acid, and 23% was present in the humin. Furthermore 38.8% of the 15N present in the composted material could be allotted to cond...
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Characterization of 15N-TNT Residues After an Anaerobic/Aerobic Treatment of Soil/Molasses Mixtures by Solid-State 15N NMR Spectroscopy. 1. Determination and Optimization of Relevant NMR Spectroscopic Parameters
Environmental Science & Technology, 1999Co-Authors: Heike Knicker, D. Bruns-nagel, Oliver Drzyzga, Eberhard Von Löw, Klaus SteinbachAbstract:Solid-state 15N NMR was applied to a humic acid, extracted from 15N-2,4,6-trinitrotoluene (TNT) enriched soil treated in an anaerobic/aerobic composting system to characterize the nitrogen functionality of the transformation products bound to the soil organic material. Signals assignable to aniline derivatives and condensation products were identified, indicating that the anaerobic/aerobic treatment caused a reduction of nitro groups followed by condensation reactions with the soil organic material. Relevant parameters for routine application of the cross polarization magic angle spinning technique were determined and optimized. The proton spin-lattice relaxation times of all peaks in the 15N NMR spectrum of the humic acid did not exceed 30 ms. Due to the fast relaxation, the application of 15N NMR Spectroscopy to soils with lower enrichment of 15N-TNT is feasible. The influence of spinning sidebands on the intensity distribution was shown to be minimal at spinning speeds between 5.5 and 6.5 kHz. Contact ...
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characterization of 15N tnt residues after an anaerobic aerobic treatment of soil molasses mixtures by solid state 15N NMR Spectroscopy 1 determination and optimization of relevant NMR spectroscopic parameters
Environmental Science & Technology, 1999Co-Authors: Heike Knicker, Oliver Drzyzga, Eberhard Von Löw, D Brunsnagel, Klaus SteinbachAbstract:Solid-state 15N NMR was applied to a humic acid, extracted from 15N-2,4,6-trinitrotoluene (TNT) enriched soil treated in an anaerobic/aerobic composting system to characterize the nitrogen functionality of the transformation products bound to the soil organic material. Signals assignable to aniline derivatives and condensation products were identified, indicating that the anaerobic/aerobic treatment caused a reduction of nitro groups followed by condensation reactions with the soil organic material. Relevant parameters for routine application of the cross polarization magic angle spinning technique were determined and optimized. The proton spin-lattice relaxation times of all peaks in the 15N NMR spectrum of the humic acid did not exceed 30 ms. Due to the fast relaxation, the application of 15N NMR Spectroscopy to soils with lower enrichment of 15N-TNT is feasible. The influence of spinning sidebands on the intensity distribution was shown to be minimal at spinning speeds between 5.5 and 6.5 kHz. Contact ...
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Solid-State 15N NMR Spectroscopy of coal
Energy & Fuels, 1995Co-Authors: Heike Knicker, Patrick G. Hatcher, Alan W. ScaroniAbstract:Solid-state 15 N NMR is applied in a study of various coal samples to evaluate the forms of nitrogen in coal. The spectra display the main signal intensities in the region of pyrrole and indole derivatives. No signals assigned to pyridine derivatives were identified. This contradicts the most common belief that pyridine-like structures comprise the major form of nitrogen in coal. The successful application of 15 N NMR Spectroscopy to coal samples may help to provide a new level of understanding of coal-nitrogen chemistry.
Jiří Kaleta - One of the best experts on this subject based on the ideXlab platform.
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Regular Two-Dimensional Arrays of Surface-Mounted Molecular Switches: Switching Monitored by UV-vis and NMR Spectroscopy.
Journal of the American Chemical Society, 2020Co-Authors: Carina Santos Hurtado, Guillaume Bastien, Milan Mašát, Jakub Radek Štoček, Martin Dračínský, Igor Rončević, Ivana Císařová, Charles T. Rogers, Jiří KaletaAbstract:Using solid-state 15N NMR Spectroscopy, the cis/trans isomerization in a two-dimensional (2-D) array of surface-mounted azobenzene-based switches was detected for the first time. In order to achiev...
Radek Marek - One of the best experts on this subject based on the ideXlab platform.
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15N NMR Spectroscopy in Structural Analysis: An Update(2001-2005)
Current Organic Chemistry, 2007Co-Authors: Radek Marek, Antonin Lycka, Erkki Kolehmainen, Elina Sievänen, Jaromír ToušekAbstract:Since our previous review article (Curr. Org. Chem. 2002, 6, 35), significant improvements and an array of 15N NMR applications in structural analysis have been published. This report aims to update coverage of improvements in methodology and various types of applications published over the period 2001 - 2005. Substantial progress in cryogenic probe technology and the commercial availability of cryoprobes have facilitated the measurement of 15N NMR parameters. The number of solid-state applications has increased significantly during the past few years. In contrast to our previous review, this article covers 15N solid-state studies. The 15N NMR chemical shifts of organic molecules are routinely measured by using cross-polarization magic-angle spinning (CP/MAS) techniques. The principal values of the chemical shift tensors can also be determined. 1H-15N and 2H-15N distance measurements made by means of 1H detection are currently used in NMR crystallography. User friendly quantum chemical programs allow for the routine calculation of 15N chemical shielding and indirect spin-spin coupling constants, especially using density functional theory (DFT). Applications of 15N NMR Spectroscopy in various fields of chemistry are summarized here. Major sections represent tautomerism, complexation, protonation, and hydrogen bonding. The other topics comprise N-alkylation, N-oxidation, regioisomerism, and changes in configuration or conformation.
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15N NMR Spectroscopy in Structural Analysis
Current Organic Chemistry, 2002Co-Authors: Radek Marek, Antonin LyckaAbstract:The implementation of both the directly and the inversely detected 15N NMR techniques at the natural abundance level of the 15N isotope is demonstrated for a diverse array of structural problems in organic chemistry. Following the application of 15N NMR to the elucidation of the structures of natural compounds and synthetic products, the 15N-detected electron distribution in such molecules and following their reactions with other molecules and ions is discussed. A significant part of the 15N structural analysis is devoted to the description of tautomers, rotamers, conformers, configurational isomers, and regioisomers. The changes in the 15N parameters induced in structurally related compounds are described briefly. At present, the optimum probe-tube-sample configuration makes it possible to acquire inverse-detected 1H-15N correlation spectra on samples, where the total available sample is limited to amounts of < 1 mg (for molecules [sim] 400 MHz). 15N NMR Spectroscopy at the natural abundance level of 15N nuclei has become a powerful tool which has substantially extended the analytical arsenal of organic chemists.
José Elguero - One of the best experts on this subject based on the ideXlab platform.
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Observation of Diastereotopic Signals in 15N NMR Spectroscopy
Angewandte Chemie (International ed. in English), 2015Co-Authors: Ibon Alkorta, Christophe Dardonville, José ElgueroAbstract:The first example in the literature of a compound showing anisochronous 15N atoms resulting from diastereotopicity is described. Racemic 1,3-dimethyl-2-phenyloctahydro-1H-benzimidazole was prepared and studied by 1H, 13C and 15N NMR Spectroscopy. If convenient conditions were used (monitored by theoretical calculations of 2JN-H spin–spin coupling constants), two 15N NMR signals were observed and corresponded to the diastereotopic atoms. GIAO/density-functional calculations of chemical shifts were not only in good agreement with the experimental values but also served as prediction tools. This study suggests that 15N NMR Spectroscopy could be used to probe chirality.
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Protonation Studies of Schiff Bases Using 13 C and 15 N-NMR Spectroscopy
Proceedings of The 10th International Electronic Conference on Synthetic Organic Chemistry, 2006Co-Authors: Almudena Perona, Rosa Ma Claramunt, Dionisia Sanz, Elena Pinilla, María R. Torres, José ElgueroAbstract:13C and 15N-NMR Spectroscopy provides clear evidence that the Schiff bases of 3-hydroxy-4-pyridinecarboxaldehyde exist as a mixture of hydroxyimino and oxoenamino tautomers in acid media. The study of the stabilities of the tautomeric forms has been approached using density functional calculations (B3LYP/6-31G**). The X-ray molecular structure of (E)-4-[(4-bromophenylimino)methyl]-3- hydroxypyridinium tetrafluoroborate has been solved.
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Study of the Structure of 1-Hydroxymethylindazole and 1-Hydroxymethylbenzotriazole by X-ray crystallography, Multinuclear NMR in Solution and DFT Calculations
Journal of Heterocyclic Chemistry, 2004Co-Authors: Ibon Alkorta, José Elguero, Nadine Jagerovic, Alain Fruchier, Glenn P. A. YapAbstract:1-Hydroxymethylindazole and 1-hydroxymethylbenzotriazole have been studied in solution by 1H, 13C and 15N NMR Spectroscopy and the X-ray structure of the second compound determined. DFT and GIAO calculations have been used to discuss geometries, energies (comparatively with 2-substituted isomers) and NMR chemical shifts.
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Intermolecular proton transfer in host–guest crystals: the case of pyrazole included in 1,1-di(2,4-dimethylphenyl)but-2-yn-1-ol, an X-ray and solid-state 13C/15N NMR study
J. Chem. Soc. Chem. Commun., 1993Co-Authors: Fumio Toda, Koichi Tanaka, Concepción Foces-foces, Antonio L. Llamas-saiz, Hans-heinrich Limbach, Francisco Aguilar-parrilla, Rosa Ma Claramunt, Concepción López, José ElgueroAbstract:The first example of a cyclic intermolecular solid-state proton transfer involving nitrogen and oxygen atoms is described, which takes place in a cyclic 2 :2 complex formed by inclusion of pyrazole in the host, 1,1-di(2,4-dimethylpheny)but-2-yn-1-ol; the system has been studied by a combination of X-ray crystallography and dynamic high resolution solid-state 13C/15N NMR Spectroscopy.
