Nuclear magnetic resonance relaxation time, chemical

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. 

Nuclear magnetic resonance (NMR) spectroscopy is a most effective and significant method for observing the structure and dynamics of polymer chains both in solution and in the solid state [1]. Undoubtedly the widest application of NMR spectroscopy is in the field of structure determination. The identification of certain atoms or groups in a molecule as well as their position relative to each other can be obtained by one-, two-, and three-dimensional NMR. Of importance to polymerization of vinyl monomers is the orientation of each vinyl monomer unit to the growing chain tacticity. The time scale involved in NMR measurements makes it possible to study certain rate processes, including chemical reaction rates. Other applications are isomerism, internal relaxation, conformational analysis, and tautomerism. 

To fully understand the performance of amorphous materials, it is necessary to be able to measure the molecular mobility of the samples on interest. This is because at temperatures as far as 50 K below the glass transition temperature, pharmaceutical glasses exhibit significant molecular mobility that can contribute to both chemical and physical instability.The main techniques that have been developed for monitoring molecular motions in amorphous materials are nuclear magnetic resonance (NMR) and calorimetric techniques (e.g., DSC and isothermal microcalorimetry). Average molecular relaxation times and relaxation time distribution functions obtained from these... 

Nuclear magnetic resonance, which is sensitive to short-range order, has been recently used to obtain information on the structure of pores. Two main techniques can be found in the literature [75] one is based on the study of NMR relaxation times of a fluid inside pores and the other on the chemical shift of e trapped in the material. 

Nuclear magnetic resonance (NMR) Chemical shift, nuclear coupling constants, relaxation times For paramagnetic proteins enhanced chemical shift resolution, contact and dipolar shifts, spin delocalisation, magnetic coupling from temperature dependence of shifts. 

A wide variety of chemical and spectroscopic techniques has been used to determine functionality in humic substances. Although nuclear magnetic resonance (NMR) spectroscopy has been used for a much shorter period of time than most other techniques for determining functional group concentrations, this technique has provided far more definitive information than all other methods combined. However, substantially more work must be done to obtain the quantitative data that are necessary for both structural elucidation and geochemical studies. In order to increase the accuracy of functional group concentration measurements, the effect of variations in nuclear Overhauser enhancement (NOE) and relaxation times must be evaluated. Preliminary results suggest that spectra of fractions isolated from humic substances should be better resolved and more readily interpreted than spectra of unfractionated samples. 

Nuclear magnetic resonance (NMR) spectroscopy has been applied to elucidate metal-binding mechanisms to organic ligands mainly by two approaches by measuring the effects of metal complexation on either the relaxation times of H of water molecules solvating the metal cation or on the chemical shifts of NMR-active metal ions (e.g.. Cd, Al, and Pb) (e.g., Connors, 1987 Wilson, 1989 Macomber, 1998). Relatively few and sparse studies have been performed by NMR on metal-HS complexes. A comprehensive and updated review has been provided by Kmgery et al. (2001) on the various applications of NMR spectroscopy to the study of metal-HS interactions. 

K. A. Christensen, D. M. Grant, E. M. Schulman, and C. Walling, Optimal determination of relaxation times of Fourier transform nuclear magnetic resonance. Determination of spin-lattice relaxation times in chemically polarized species, J. Phys. Chem. 78, 1971-1977 (1974). 

Nuclear magnetic resonance has been shown to be a most effective method for the study of lipid chemistry (Chapman, 1965 1972 Henrikson, 1971). With the advent of commercially available fast Fourier transform spectrometers, high resolution natural abundance 1 3 C spectra and relaxation times of lipids have become relatively commonplace. Utilization of these 1 3C nmr techniques has yielded a considerable amount of information concerning the mobility and organization of lipids in liquid crystals and membranes (Oldfield and Chapman, 1971). 13C Chemical shifts of lipids are given in Table 21. The rest of this discussion will be devoted to the interpretation of these results. 

Nuclear Magnetic Resonance Spectroscopy.—As noted above, conformational analysis of bicyclo[3.3.1]nonanes is still a topic of considerable interest. A variable-temperature n.m.r. analysis now provides the first case in which the boat-chair-chair-boat equilibrium is directly observed in the amines (17) and (18). In a related case, re-examination of the acetal (19) suggests that the preferred conformation involves a chair carbocyclic ring and a boat heterocyclic ring. This conclusion was made by n.m.r. analysis, using lanthanide shift reagents, by a study of nuclear Overhauser effects, and by measurement of relaxation times of protons. Details have been reported for other 3-azabicyclo[3.3.1]nonanes, and the non-additivity of substituent effects on chemical shifts in 9-thiabicyclo[3.3.1]non-2-enes has been analysed. Both and n.m.r. data have been reported for a series of 9-borabicyclo[3.3.1]non-anes and their pyridine complexes. 

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