Nuclear coupling resonance

J A measure of the coupling constant in nuclear magnetic resonance. 

Venanzi T J 1982 Nuclear magnetic resonance coupling constants and electronic structure in molecules J. Chem. Educ. 59 144-8... 

Di Bari L, Kowalewski J and Bodenhausen G 1990 Magnetization transfer modes in scalar-coupled spin systems investigated by selective 2-dimensional nuclear magnetic resonance exchange experiments J. Chem. Rhys. 93 7698-705... 

Farrar T C and Stringfellow T C 1996 Relaxation of transverse magnetization for coupled spins Encyclopedia of Nuclear Magnetic Resonance ed D M Grant and R K Harris (Chichester Wiley) pp 4101-7... 

Specinfo, from Chemical Concepts, is a factual database information system for spectroscopic data with more than 660000 digital spectra of 150000 associated structures [24], The database covers nuclear magnetic resonance spectra ( H-, C-, N-, O-, F-, P-NMR), infrared spectra (IR), and mass spectra (MS). In addition, experimental conditions (instrument, solvent, temperature), coupling constants, relaxation time, and bibliographic data are included. The data is cross-linked to CAS Registry, Beilstein, and NUMERIGUIDE. 

The section on Spectroscopy has been retained but with some revisions and expansion. The section includes ultraviolet-visible spectroscopy, fluorescence, infrared and Raman spectroscopy, and X-ray spectrometry. Detection limits are listed for the elements when using flame emission, flame atomic absorption, electrothermal atomic absorption, argon induction coupled plasma, and flame atomic fluorescence. Nuclear magnetic resonance embraces tables for the nuclear properties of the elements, proton chemical shifts and coupling constants, and similar material for carbon-13, boron-11, nitrogen-15, fluorine-19, silicon-19, and phosphoms-31. 

Generally, the most powerful method for stmctural elucidation of steroids is nuclear magnetic resonance (nmr) spectroscopy. There are several classical reviews on the one-dimensional (1-D) proton H-nmr spectroscopy of steroids (267). C-nmr, a technique used to observe individual carbons, is used for stmcture elucidation of steroids. In addition, C-nmr is used for biosynthesis experiments with C-enriched precursors (268). The availability of higher magnetic field instmments coupled with the arrival of 1-D and two-dimensional (2-D) techniques such as DEPT, COSY, NOESY, 2-D J-resolved, HOHAHA, etc, have provided powerful new tools for the stmctural elucidation of complex natural products including steroids (269). 

Nuclear Magnetic Resonance Spectroscopy. Nmr is a most valuable technique for stmeture determination in thiophene chemistry, especially because spectral interpretation is much easier in the thiophene series compared to benzene derivatives. Chemical shifts in proton nmr are well documented for thiophene (CDCl ), 6 = 7.12, 7.34, 7.34, and 7.12 ppm. Coupling constants occur in well-defined ranges J2-3 = 4.9-5.8 ... 

Other spectroscopic methods such as infrared (ir), and nuclear magnetic resonance (nmr), circular dichroism (cd), and mass spectrometry (ms) are invaluable tools for identification and stmcture elucidation. Nmr spectroscopy allows for geometric assignment of the carbon—carbon double bonds, as well as relative stereochemistry of ring substituents. These spectroscopic methods coupled with traditional chemical derivatization techniques provide the framework by which new carotenoids are identified and characterized (16,17). 

The most common detectors in HPLC are ultraviolet, fluorescence, electrochemical detector and diffractometer. However, despite all improvements of these techniques it seems necessary to have a more selectivity and sensitivity detector for the purposes of the medical analysis. It should be therefore improvements to couple analytical techniques like infrared IR, MS, nuclear magnetic resonance (NMR), inductively coupled plasma-MS (ICP-MS) or biospecific detectors to the LC-system and many efforts have been made in this field. 

T. P. Das and E. L. Hahn, Nuclear Quadrupole Resonance Spectroscopy, Academic Press, New York, 1958, 223 pp E. A. C. Lucken, Nuclear Quadrupole Coupling Constants, Academic Press, London, 1969, 360 pp. 

Quadrupole coupling constants for molecules are usually determined from the hyperfine structure of pure rotational spectra or from electric-beam and magnetic-beam resonance spectroscopies. Nuclear magnetic resonance, electron spin resonance and Mossbauer spectroscopies are also routes to the property. There is a large amount of experimental data for and halogen-substituted molecules. Less data is available for deuterium because the nuclear quadrupole is small. 

Pusecker K, J Schewitz, P Gfrorer, L-H Tseng, K Albert, E Bayer (1998) On-line coupling of capillary electrochromatography, capillary electrophoresis, and capillary HPLC with nuclear magnetic resonance spectroscopy. Anal Chem 70 3280-3285. 

LC-MS/MS Liquid chromatography coupled with tandem mass spectrometry LC-NMR Liquid chromatography coupled with nuclear magnetic resonance TLC Thin-layer chromatography... 

Helgaker, T., Watson, M., Handy, N. C., 2000, Analytical Calculation of Nuclear Magnetic Resonance Indirect Spin-Spin Coupling Constants at the Generalized Gradient Aproximation and Hybrid Levels of Density Functional Theory , J. Chem. Phys., 113, 9402. 

Malkina, O. L., Salahub, D. R., Malkin, V. G., 1996, Nuclear Magnetic Resonance Spin-Spin Coupling Constants from Density Functional Theory Problems and Results , J. Chem. Phys., 105, 8793. 

Abel, C.B.L., Lindon, J.C., Noble, D., Rudd, B.A.M., Sidebottom, P.J., and Nicholson, J.K, Characterization of metabolites in intact Streptomyces citricolor culture supernatants using high-resolution nuclear magnetic resonance and directly coupled high-pressure liquid chromatography-nuclear magnetic resonance spectroscopy, Anal. Biochem., 270, 220, 1999. 

Riickert, M., Wohlfarth, M., and Bringmann, G., Characterization of protein mixtures by ion-exchange chromatography coupled on-line to nuclear magnetic resonance spectroscopy, ]. Chromatogr. A, 840, 131, 1999. 

The problem of characterizing the three-dimensional structure of G-protein-coupled receptors by x-ray crystallography or nuclear magnetic resonance (NMR) has been particularly difficult to solve. The receptors are complicated membrane proteins that are difficult to produce in sufficiently large quantities. When they have been available, it has been difficult to make them form useful... 

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