Nuclear magnetic resonance spectroscopy shielding

Nuclear magnetic resonance spectroscopy gives precise information on complexation in solution. Equilibrium is rapidly established on an NMR time scale, hence only an average spectrum is observed and it is difficult to determine the spectrum of a pure complex. When complexation of a sugar or polyol with a diamagnetic ion occurs, all of the signals shift downfield. Equation (11.1) allows the variation of the shielding constant Ao- of the proton to be calculated when the nucleus is subjected to an electric field E whose projection on the C-H bond is... 

Nuclear magnetic resonance spectroscopy is such a powerful tool for stracture determination because protons in different environments experience different degrees of shielding and have different chemical shifts. In compounds of the type CH3X, for example, the shielding of the methyl protons increases as X becomes less electronegative. Inas-... 

It is our good fortune that NMR has layers of complexity that are not explicitly revealed in Eqs. (1) and (2). Unraveling this complexity (shielding, coupling, relaxation) has been the preoccupation of NMR spectroscopists for more than half a century, and is the topic of this section of the Handbook. Three chapters on nuclear magnetic resonance spectroscopy are assembled. They are authored by outstanding experimentalists working at the forefront of NMR research. 

JG Oldenziel, NJ Trappeniers. High resolution nuclear magnetic resonance spectroscopy in liquids and gases at pressures up to 2500 bar, HI. Density dependence of the proton magnetic shielding constants in the polar liquids methanol and ethanol. Physica A 83 161-172, 1976. 

Figure 8 Dependence of the i29Xe chemical shift (negative shielding) upon the number of xenon atoms adsorbed per gram of zeolite. Fraissard J (1996) In Grant DM and Harris RK (eds) Encyclopedia of Nuclear Magnetic Resonance Spectroscopy, Vol. 5, pp. 3058-3064. Chichester Wiley John Wiley Sons Limited. Reproduced with permission.

A different class of phenomena can be related to the interaction of the electronic polarization density and induced current with the nuclei. Thus the chemical shifts in nuclear magnetic resonance (NMR) spectroscopy are interpreted in terms of magnetic shielding of the electrons, perturbed by a static magnetic field, at those nuclei possessing an intrinsic magnetic moment [7]. 

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