NMR frequency

Nuclide Natural abundance, % Spin I Sensitivity at constant field relative to NMR frequency for a 1-kG field, Mffz Magnetic moment J-T-1 Electric quadrupole moment Q, 10 m ... 

Isotope Natural abundance (%) Nuclear spin Electric quadrupole moment NMR frequency fora 23.5 kO field (MHz) Relative sensitivity... 

Isotope Nuclear spin quantum no. I NMR frequency rel to H(SiMe4) = 100.000 Relative receptivity D ( Nuclear quadmpole moment Q (e 10-2 ... 

The deuteron solid state spectra are completely dominated by the quadrupole coupling of the deuteron I = 1 spin, the NMR frequency being given by lS)... 

In presence of molecular motion the NMR line shape will change. A particularly simple situation arises, if the motion is rapid on timescale defined by the inverse width of the spectrum in absence of motion 6 1. In this fast exchange limit, which in 2H NMR is reached for correlation times tc < 1CT7 s, the motion leads to a partially averaged quadrupole coupling and valuable information about the type of motion can directly be obtained from analysis of the resulting line shapes. The NMR frequency is then given by... 

Fig. 7. Theoretical line shapes resulting from an interchange between two NMR frequencies

In absence of motion the formation of the solid echo is limited by T only, in presence of motions, however, the NMR frequencies in the periods of destructive interference and constructive refocussing, respectively, may be different. The signal following the refocussing pulse is given by27)... 

Fig. 3.7.7 (A) NMR frequency spectra of different blood samples. The linewidths were found to be 70, 15 and 10 Hz for packed, crushed erythrocyte and plasma samples, respectively. (B) DDIF (solid line) and inversion recovery (dashed line) spectra obtained for the packed erythrocyte sample.

The difference in resonance NMR frequency of a chemically shielded nucleus measured relative to that of a suitable reference compound is termed chemical shift [164,165], and is a measure of the immediate electromagnetic environment of a nucleus. While the chemical shift depends on the Bo field, J does not. Chemical shifts, which cover a range of about 10 ppm for protons (i.e. 600 Hz in case of a 14.1 kG magnetic field) and 250 ppm for 13C, are the substance of NMR. 

In cases where 2D NMR experiments are insufficient for a complete analysis of anionic surfactant mixtures, LC-NMR may provide better information. Characterisation of fatty alcohol ethoxylate (FAE) based oligomeric surfactants by on-line 2D (GCOSY, TOCSY and Homo 2DJ) stopped-flow HPLC- H NMR has been described [655,656]. The analysis of a typical mixture comprising three components (PEG and PEOs with different end-groups) is shown in Figure 7.34. In this representation, the 111 NMR frequency domain is in the... 

This effect is caused by an RF pulse through a conductor such as the NMR coil in a magnetic field Acoustic ringing increases at lower NMR frequencies and special pulse sequences are used to suppress it. 

Viscosity and molar mass measurements for 70 and 71 supplemented with broad H-NMR signals which depended on concentration, temperature, and solvent but independent of NMR frequency, strongly suggested self-association of these macromolecules (in a CHC13 solution). 

NMR spectroscopy is a powerful technique to study molecular structure, order, and dynamics. Because of the anisotropy of the interactions of nuclear spins with each other and with their environment via dipolar, chemical shift, and quadrupolar interactions, the NMR frequencies depend on the orientation of a given molecular unit relative to the external magnetic field. NMR spectroscopy is thus quite valuable to characterize partially oriented systems. Solid-state NMR... 

More recently, three-dimensional (3D) pulse sequences with DOSY have been presented where a diffusion coordinate is added to the conventional 2D map. As in the conventional 2D spectra, these experiments reduce the probability of signal overlap by spreading the NMR frequency of the same species over a 2D plane, and distribute the diffusion coefficient. 

When the nuclear motion is a random proceas, one obtains, for (i), from the theory of random processes (61) the normalized spectral density of the mean square dipolar magnetic field versus frequency (3). The spectral density near a NMR frequency is proportional to the probability of a... 

Fio. 5. Spectral density caused by Brownian-type motions versus frequency, tc is the correlation time for the random motion and ro is a NMR frequency. 

The effective field experienced by a nucleus in a chemical compound is generally different from the applied field due to the shielding by the distribution of electrons around the nucleus. A shift in NMR frequency, known as the chemical shift, proportional to applied field results. For closed... 

Fig. 11. A powder pattern of Al NMR in a- AI2O1 at NMR frequency of 7.20 me./ second (/fg = 6490 gauss) the magnetic field increases from left to right with a total scan of about 1500 gauss. This is the dispersion mode audio signal at Hi = 0.5 gauss and is the absorption envelope except at certain points as described in Section II,C,2 109).

Two-Dimensional NMR—Basically, the two-dimensional NMR techniques of nuclear Overhauser effect spectroscopy (NOESY) and correlation spectroscopy (COSY) depend on the observation that spins on different protons interact with one another. Protons that are attached to adjacent atoms can be directly spin-coupled and thus can be studied using the COSY method. This technique allows assignment of certain NMR frequencies by tracking from one atom to another. The NOESY approach is based on the observation that two protons closer than about 0.5 nm perturb one another s spins even if they are not closely coupled in the primary structure. This allows spacial geometry to be determined for certain molecules. 

Nuclide Spin I Electric quadmpole moment eQ (10-2 m2) Natural abundance (%) Relative sensitivity Gyromagnetic ratio y (103 radT- S-l)a NMR frequency (MHz) Bo = 2.3488 T)3... 

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