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15N NMR Spectroscopy

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Antonin Lycka – One of the best experts on this subject based on the ideXlab platform.

  • 15N NMR Spectroscopy in Structural Analysis: An Update(2001-2005)
    Current Organic Chemistry, 2007
    Co-Authors: Radek Marek, Antonin Lycka, Erkki Kolehmainen, Elina Sievänen, Jaromír Toušek
    Abstract:

    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.

  • 15N NMR Spectroscopy in Structural Analysis
    Current Organic Chemistry, 2002
    Co-Authors: Radek Marek, Antonin Lycka
    Abstract:

    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.

Jiří Kaleta – One of the best experts on this subject based on the ideXlab platform.

Radek Marek – One of the best experts on this subject based on the ideXlab platform.

  • 15N NMR Spectroscopy in Structural Analysis: An Update(2001-2005)
    Current Organic Chemistry, 2007
    Co-Authors: Radek Marek, Antonin Lycka, Erkki Kolehmainen, Elina Sievänen, Jaromír Toušek
    Abstract:

    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.

  • 15N NMR Spectroscopy in Structural Analysis
    Current Organic Chemistry, 2002
    Co-Authors: Radek Marek, Antonin Lycka
    Abstract:

    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.

  • Observation of Diastereotopic Signals in 15N NMR Spectroscopy
    Angewandte Chemie (International ed. in English), 2015
    Co-Authors: Ibon Alkorta, Christophe Dardonville, José Elguero
    Abstract:

    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 15NNMR Spectroscopy. If convenient conditions were used (monitored by theoretical calculations of 2JN-H spin–spin coupling constants), two 15NNMR 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 15NNMR Spectroscopy could be used to probe chirality.

  • Protonation Studies of Schiff Bases Using 13 C and 15 N-NMR Spectroscopy
    Proceedings of The 10th International Electronic Conference on Synthetic Organic Chemistry, 2006
    Co-Authors: Almudena Perona, Rosa Ma Claramunt, Dionisia Sanz, Elena Pinilla, María R. Torres, José Elguero
    Abstract:

    13C and 15NNMR 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.

  • 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, 2004
    Co-Authors: Ibon Alkorta, José Elguero, Nadine Jagerovic, Alain Fruchier, Glenn P. A. Yap
    Abstract:

    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.