Line widths in nmr spectra

Using a solvent-reagent system gives narrow line-widths in NMR spectra of phospholipid extracts when applied to human amniotie fluid. Resolution of the major components is achieved by manipulating... 

Figure 7. Concentration dependence of the line widths in NMR spectra of the complexes ...

It will be interesting to test the generality of the results obtained so far. For example, the NMR spectra of adsorbed species were dominated by a distribution in chemical shift rather than a distribution in line width. On the other hand, the NMR spectra of polymers themselves were dominated by a distribution in line width. 13c NMR spectra of polymers often offer well-separated broad lines, for which DISPA analysis should be especially informative, and for which conventional line shape analysis experiments may be extremely time-consuming. 

Recently two-dimensional solid-state heteronuclear chemical shift correlation experiments involving magic angle sample spinning (MASS) have been described. This technique results in an increase in the resolution of solid-state proton spectra by a factor of 5-10. Solid-state NMR spectroscopy has hitherto been confined to C-NMR spectra since the residual line widths in the spectra of solid samples are around 2 ppm, so that only four or five nonequivalent protons can be distinguished in the normal proton spectral region of 10-15 ppm. The increase in resolution attained by the 2D solid-state heteronuclear COSY experiment should promote further studies of the H-NMR spectra of solid samples. 

In this case ESR spectra at 77°K and 300°K cannot be observed (either in solution or in powder), for Ni(II) complexes norCu(II) complexes. On the other hand, well-resolved NMR spectra have been recorded for all complexes. Line widths in the spectra of the Cu(II) and Ni(II) complexes... 

ESR line widths are also sensitive to processes that modulate the g-value or hyperfine coupling constants or limit the lifetime of the electron spin state. The effects are closely analogous to those observed in NMR spectra of dynamical systems. However, since ESR line widths are typically on the order of 0.1-10 G... 

Line shape analysis was performed for the binding of some dihydroxycholate ions to /1-cyclodextrin.205 The dihydroxycholates show different 18-CH3 signals for the complexed and free dihydroxycholate ions. To extract exchange rate constants from the NMR spectra, a complete line-shape simulation was performed. The simulation requires input of the chemical shift difference between the two sites, the line width in the absence of exchange, the residence time in each site (thg and Tg), and the relative population (fHG and fG) of each site (Equation (11)). The values were varied until the simulated and experimental spectra could be superimposed. The dissociation rate... 

Composite-pulse decoupling schemes like WALTZ [36, 37], DIPSI [38], or GARP [39], which are used in solution-state NMR, have failed to offer any significant improvements in the solid state compared to CW decoupling. The residual line width in CW-decoupled spectra is dominated by a cross term between the chemical-shielding tensor of the protons and the heteronuclear dipolar-coupling tensor [40, 41]. 

It should be noted that the activation energies for motional processes in the same crosslinked polymer gel calculated from line widths in 13C NMR spectra are higher than those calculated from 1H NMR spectra under the magic angle conditions (residual line width). These findings indicate that 13C line widths (which are of the order of 10 Hz) are probably more affected by sample inhomogeneity and by relatively small residual chemical shift anisotropies 162). 

The non-rotation of the sapphire flow cell, together with the detection volume and the employed flow rate, determine the resulting NMR line width. Whereas with rotation of the NMR tube in a conventional NMR probe, the signal line width of chloroform at the height of the 13C satellites in degassed acetone-d6 is about 3-4 Hz, SFC continuous-flow probes show values of the order of 15-18 Hz in the liquid and in the supercritical state. This hump test also indicates that there is no change in the signal line width in the H NMR spectra in the liquid and in the supercritical state. 

Figure 14 Experimental 170 stationary NMR spectra for [170]-L-aianine, recorded at (A) 9.4, (B) 11.7, (C) 16.4 and (D) 21.6 T. Each spectral line width in frequency unit, SW, is also given.

Observable NMR spectral parameters such as chemical shift, spin-spin coupling, and peak intensities in simple ID spectra allow one to obtain polymer composition, tacticity, sequence distribution, and mechanism of polymerization. However, the poor mobility of polymers often leads to high viscosity solutions and rapid Tj relaxation, resulting in the poor spectral resolution. The viscosity can be decreased by dilution and high measurement temperature. Fortunately, many polymers possess segmental mobility, which facilitates the observation of high-resolution spectra with the line widths in the range of 1-10 Hz. 

The experiments were prepared In the same way as described for the polymerisation studies on a vacuum line. The dynamic NMR spectra were recorded starting from the lowest temperature. Simula tlons of the spectra were made using the DNMR 3 program. The exchange rate constant was assumed to be the value which gave the most similar simulated spectrum. Such parameters as signal width and maximum and saddle Intensity ratios were compared. Accuracy of determination of exchange rate constant was better than 5Z. 

The second major contributor to NMR line widths in spectra of solid materials is chemical shift anisotropy, CSA. CSA results... 

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