Nuclear magnetic resonance proton coupling

Albert, K. 1997. Supercritical fluid chromatography— proton nuclear magnetic resonance spectroscopy coupling. Journal of Chromatography A, 785 65-83. 

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 ... 

If one wishes to obtain a fluorine NMR spectrum, one must of course first have access to a spectrometer with a probe that will allow observation of fluorine nuclei. Fortunately, most modern high field NMR spectrometers that are available in industrial and academic research laboratories today have this capability. Probably the most common NMR spectrometers in use today for taking routine NMR spectra are 300 MHz instruments, which measure proton spectra at 300 MHz, carbon spectra at 75.5 MHz and fluorine spectra at 282 MHz. Before obtaining and attempting to interpret fluorine NMR spectra, it would be advisable to become familiar with some of the fundamental concepts related to fluorine chemical shifts and spin-spin coupling constants that are presented in this book. There is also a very nice introduction to fluorine NMR by W. S. and M. L. Brey in the Encyclopedia of Nuclear Magnetic Resonance.1... 

Below we report methodological studies based upon HPLC, GC/FID, GC-MS, LC-MS, matrix-assisted laser desorption ionisation coupled with time-of-flight mass spectrometry (MALDI-ToF/MS), CE, proton nuclear magnetic resonance ( I INMR), RIA and enzymatic colorimetric techniques. 

Nuclear magnetic resonance (NMR) has proved to be a very useful tool for structural elucidation of natural products. Recent progress in the development of two-dimensional 1H- and 13C-NMR techniques has contributed to the unambiguously assignment of proton and carbon chemical shifts, in particular in complex molecules. The more used techniques include direct correlations through homonuclear (COSY, TOCSY, ROESY, NOESY) [62-65] and heteronuclear (HMQC, HMBC) [66. 67] couplings. 

The structures of vanicosides A (1) and B (2) and hydropiperoside (3) were established primarily by one- and two-dimensional nuclear magnetic resonance (NMR) spectroscopy techniques and fast atom bombardment (FAB) mass spectrometry (MS).22 The presence of two different types of phenylpropanoid esters in 1 and 2 was established first through the proton (4H) NMR spectra which showed resonances for two different aromatic substitution patterns in the spectrum of each compound. Integration of the aromatic region defined these as three symmetrically substituted phenyl rings, due to three p-coumaryl moieties, and one 1,3,4-trisubstituted phenyl ring, due to a feruloyl ester. The presence of a sucrose backbone was established by two series of coupled protons between 3.2 and 5.7 ppm in the HNMR spectra, particularly the characteristic C-l (anomeric) and C-3 proton doublets... 

The nuclear magnetic resonance (NMR) spectrum of chrom-3-ene (1) has been measured13 and the sign of coupling constants between protons on the hetero ring obtained from a study of double quantum transitions.13 An inter-ring coupling (J4 8) has been detected.14-16 In... 

Figure 9-37 Nuclear magnetic resonance spectrum of C9H10 at 60 MHz. The calibrations are relative to the protons of TMS. The insets show the peaks centered on 321, 307, and 119 Hz with an expanded scale. The spacing between the peaks is 1.5 Hz for Group B at 307 Hz, and 0.75 Hz for Groups A and C at 321 and 119 Hz. The C6H5 protons are coupled to each other, not to A, B, or C.

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