Nuclear magnetic resonance spectroscopy relaxation parameters

Nuclear magnetic resonance spectroscopy has been widely employed in the study of rotational isomer phenomena produced by substituents lacking rotational symmetry. The preferred conformations in solution have been determined by various NMR techniques, essentially (i) analysis of H and C chemical shifts regarding the orientation of the substituent (ii) analysis of stereospecific long-range coupling constants Vh,h and Vc,h (iii) relaxation parameters such as NOE and spin-lattice relaxation time (T,) (iv) LIS experiments at H and C frequencies. The results obtained... 

Several spectroscopic techniques, namely, Ultraviolet-Visible Spectroscopy (UV-Vis), Infrared (IR), Nuclear Magnetic Resonance (NMR), etc., have been used for understanding the mechanism of solvent-extraction processes and identification of extracted species. Berthon et al. reviewed the use of NMR techniques in solvent-extraction studies for monoamides, malonamides, picolinamides, and TBP (116, 117). NMR spectroscopy was used as a tool to identify the structural parameters that control selectivity and efficiency of extraction of metal ions. 13C NMR relaxation-time data were used to determine the distances between the carbon atoms of the monoamide ligands and the actinides centers. The II, 2H, and 13C NMR spectra analysis of the solvent organic phases indicated malonamide dimer formation at low concentrations. However, at higher ligand concentrations, micelle formation was observed. NMR studies were also used to understand nitric acid extraction mechanisms. Before obtaining conformational information from 13C relaxation times, the stoichiometries of the... 

Solid-state nuclear magnetic resonance (NMR) has been extensively used to assess structural properties, electronic parameters and diffusion behavior of the hydride phases of numerous metals and alloys using mostly transient NMR techniques or low-resolution spectroscopy [3]. The NMR relaxation times are extremely useful to assess various diffusion processes over very wide ranges of hydrogen mobility in crystalline and amorphous phases [3]. In addition, several borohydrides [4-6] and alanates [7-11] have also been characterized by these conventional solid-state NMR methods over the years where most attention was on rotation dynamics of the BHT, A1H4, and AlHe anions detection of order-disorder phase transitions or thermal decomposition. There has been little indication of fast long-range diffusion behavior in any complex hydride studied by NMR to date [4-11]. 

Nuclear magnetic resonance (NMR) spectroscopy has great relevance in the area of investigation of molecular structures. Many studies using NMR spectroscopy and microscopy have been reported in elastomer based systems. Due to the possibihty of reuse of samples after the analysis (NMR is nondestructive) NMR attracts many material scientists to select this technique for characterization. In the case of polymers NMR is specifically useful in finding out the crosslink density. Since the crosslink density is related to the size of pores or cavities inside solid polymers, this method points towards the structural elucidation of polymers. From the parameters such as magnetic relaxation and the dipolar correlation effect obtained from the NMR spectrum, crosslink density can be calculated. In addition to the crosslink density, the behaviour of small particles inside the polymer matrices can also be... 

Around 1950, it was discovered that nuclear resonance frequencies depend not only on the nature of the atomic nuclei, but also on their chemical environment. The possibility of using NMR as a tool for chemical analysis soon became apparent. All applications of solution NMR spectroscopy make use of one or more of the spectral parameters chemical shift, spin-spin coupling, signal intensity, and relaxation time. In the following sections examples from h and C NMR are used but the concepts described apply to magnetic nuclei in general. 

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