Low-field NMR

In spin relaxation theory (see, e.g., Zweers and Brom[1977]) this quantity is equal to the correlation time of two-level Zeeman system (r,). The states A and E have total spins of protons f and 2, respectively. The diagram of Zeeman splitting of the lowest tunneling AE octet n = 0 is shown in fig. 51. Since the spin wavefunction belongs to the same symmetry group as that of the hindered rotation, the spin and rotational states are fully correlated, and the transitions observed in the NMR spectra Am = + 1 and Am = 2 include, aside from the Zeeman frequencies, sidebands shifted by A. The special technique of dipole-dipole driven low-field NMR in the time and frequency domain [Weitenkamp et al. 1983 Clough et al. 1985] has allowed one to detect these sidebands directly. 

The value of -NMR and 13C-NMR spectroscopy in characterizing transition metal carbene complexes was noted in Section III,B,2. The carbene carbon resonance is invariably found at low field (200-400 ppm) in the 13C-NMR spectrum, while protons attached to Ca in 18-electron primary and secondary carbene complexes also resonate at low fields. NMR data for some Ru, Os, and Ir alkylidene complexes and related compounds are given in Table V. 

Bertram H C, Purslow P P and Andersen H J (2002), Relationship between meat structure, water mobility and distribution - A Low-Field NMR study , J Agric Food Chem, 50,... 

Ruan, R.R., Long, Z., Song, A., and Chen, P.L. 1998. Determination of the glass transition temperature of food polymers using low field NMR. Lebensm. Wiss. Technol 31, 516-521. 

G.H. Sprlanda, P.M. Larsena, F. Lundby, A.-P. Rudic, andT. Guiheneuf, Determination of total fat and moisture content in meat using low field NMR, Meat Sci., 66, 543-550 (2004). 

The character of the carbonyl bond gives rise to very low-field nmr absorptions for the proton of an aldehyde group (—CH=Q). As Table 9-4 (pp. 308-309) shows, these absorptions are some 4 ppm to lower fields than alkenyl hydrogens (—CH=C ). Some of this difference in shift can be ascribed to the... 

Accurate determination of the amount of solid fat in edible fats and oils is an essential requirement for process control in food industry during hydrogenation, interesterification and blending. Moreover, important physical properties, such as hardness, heat resistance, mouth-feel and flavor release, can be predicted via measurements of solid fat content at different temperatures using low resolution (low-field) NMR. 

Thybo, A. K., Andersen, H. J., Karlsson, A. H., Dqnstrup, S., and Stqdkilde-Jqrgensen, H. (2003). Low-field NMR relaxation and NMR-imaging as tools in differentiation between potato sample and determination of dry matter content in potatoes. Lebensm. Wiss. U. Technol. 36,315-322. 

Low-Field NMR Magnetisation Relaxation Experiments for Quality Control Purposes... 

Pore Structure Characterization of Catalyst Supports via Low-Field NMR Spectroscopy... 

Scheme 65) ". 212 was stable in ether solution up to 0 °C but is completely decomposed after 15 h at 25 °C, whereas it remained unchanged in toluene up to 135 °C. Gemaallene 212 was isolated by crystallization from ether at —20°C as colorless crystals, which showed a low-field NMR signal at 235.1 ppm in toluene-dg as in the case of 207. ... 

Bertram, H.C., Wiking, L., Nielsen, J.H., and Andersen, H.J. (2005). Direct measurement of phase transitions in milk fat during cooling of cream a low-field NMR approach. Int Dairy J. 15, 1056-1063. 

The use of the low-field NMR spin-lattice relaxation technique has recently been successfully demonstrated [75-80] as a pore structure tool for porous materials saturated with a solvent (usually water). The basic principle is that the portion of pore fluid near a pore wall undergoes spin-lattice (Tj) and spin-spin (Tj) relaxation in a magnetic field at a faster rate than the bulk fluid. This, coupled with the fast diffusional exchange of fluid between regions within... 

D. P. Gallegos, D. M. Smith and C.J. Brinker, A NMR technique for the analysis of pore structure application to mesopores and micropores. /. Colloid Interface Sci., 124 (1) (1988) 186. D.M. Smith and P.J. Davis, Pore analysis of vet materials via low-field NMR, in F. Rodriguez-Reinoso, J. Rouquerol, K.S.W. Sing and K.K. Unger (Eds.), Characterization of Porous Solids II, Studies in Surface Science and Catalysis Vol. 62, Proc. of the lUPAC Symposium (COPS II), Alicante, Spain, May 1990, Elsevier, Amsterdam, 1991, pp. 301-310. 

The use of low-field NMR in quality control applications has increased because of the ease of operation and reliability of the data. Most of the applications involve the measurement of Tj and/or T relaxation times, to yield quantitative information relating to the concentrations of individual components. The applications include the determination of viscosity and the measurement of moisture, fat, hydrogen, fluorine, and carbon contents. One of the most common uses of this technique is the quantitative determination of the state of water in soils, foodstuffs, coals, and catalysts. ... 

Imaging has also been applied to the study of chilling injury in persimmon fruit,312 to the study of growth and ripening of kiwi fruit,313 and to the detection of pitted olives, while a conveyer belt transports the fruits through a low-field NMR magnet.314... 

Equilibration studies on model compounds 109 showed that in those with H-3 and H-5 cis the latter proton appeared as a low-field NMR signal at ca. 

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