Wide-line NMR

Poly(vinyl fluoride) [24981-14-4] (PVF) is a semicrystaltiae polymer with a planar, zig-zag configuration (50). The degree of crystallinity can vary significantly from 20—60% (51) and is thought to be primarily a function of defect stmctures. Wide-line nmr and x-ray diffraction studies show the unit cell to contain two monomer units and have the dimensions of a = 0.857 nm, b = 0.495 nm, and c = 0.252 nm (52). Similarity to the phase I crystal form of poly (vinytidene fluoride) suggests an orthorhombic crystal (53). 

In crystallizing fatty acids, solvent polarity does not influence crystal form as much as temperature and concentration (9). Infrared (9,10) and wide-line nmr spectra (11) as well as x-ray methods (12,13) can be used to detect the various crystalline forms. 

Sample preparation requirements in solid state NMR are strikingly simple because the measurement is carried out at ambient temperature and pressure. Wide-line NMR experiments can be carried out on solid samples in any form, as far as the sample dimensions fit those of the coil in the NMR probe. MAS experiments require the material to be uniformly distributed within the rotor. 

Magnetic-susceptibility measurements showed the presence of UF4 in heated samples. Ebert et al. (E14) reported a nominal stoichiometry CisUFg, magnetic-susceptibility measurements indicating partial reduction at room temperature, with 10% of the uranium species present as U(IV). Wide-line NMR demonstrated the presence of both U(VI) and U(IV). 

Zeigler, R.C. and Maciel, GE., A study of the structure and dynamics of dimethyloctadecylsilyl-modified silica using wide-line NMR techniques, J. Am. 

Usually, in wide-line NMR experiments, the first derivative of the resonance absorption curve is obtained. Taking into account that the amplitude of this curve decreases with the square of the line width, the conclusion can be drawn from Table I that, besides the resonances from the Si sites, the contributions of the other sites should be hidden in the noise during measurement. 

Conventional single-crystal studies of aluminosilicates date back to the early 1950 s, and principal components of the quadrupole-coupling tensors together with asymmetry parameters have been determined for a number of minerals (see Table XI). Wide-line-NMR measurements of the dependence of the 27A1 and 23Na quadrupole-coupling constants in analcime and zeolites Na-X and Na-A on the water content were carried out by Gabuda et al. (137). 

Figure 3 wide line NMR spectra at 79 MHz of V loaded aluminas after dehydration in vacuo at 220°C. 

FIGURE 4 Experimental (recorded at 78.9 MHz and room temperature) and simulated 51V wide-line NMR spectra of C-Hyd-V, 5SijS and C-Hyd-V005Si/l samples. (Reproduced with permission from Dzwigaj et al. (2001).)... 

Formerly (also in the second edition of this book) the field of NMR was subdivided into the so called High-Resolution NMR (restricted to solutions) and the "broad band" or "wide line NMR (characteristic for solids). Due to the great advances in NMR techniques the barrier between these two - once quite separate - disciplines has almost disappeared. 

Another important application of wide-line NMR is the determination of crystallinity. Some polymers give spectra, which can be graphically separated into a broader and a narrower component. In this way Wilson and Pake determined the crystallinity of polyethylene and poly(tetrafluoroethylene) as early as 1953. 

Weight-average molecular mass, 18 Weissenberg effect, 526 number, 57,556 Wet fastness, 881 Wide-line NMR, 368,373, 374 WLF... 

I. BROAD IS BEAUTIFUL THE NATURE OF INFORMATION AVAILABLE FROM WIDE-LINE NMR... 

In the F wide-line NMR observations we find a single narrow component to the spectrum at room temperature. The residual line... 

By contrast, the wide-line NMR studies show evidence for both narrowed and unnarrowed components to the spectrum for both CgDg and G5D5N. A typical example, shown in Figure 3(b) for CgDg included... 

VanPutte, K., L.F. Vermas, J. VanDerEnden, and C. DerHollander, Relations Between Pulsed NMR, Wide Line NMR, and Dilatometry, Ibid. 52 179-181 (1975). 

V wide-line NMR spectra were collected on a Bmker MSL 300 FT NMR spectrometer operating at 78.9 MHz and equipped with a special probe head for measurements in the absence of air. UV-Visible-NIR diffuse reflectance spectra (DRS) were measured in air using a Perkin Elmer Lamda 19 instrument after transformation of reflectivity (R) according to the Kubelka-Munk function F(R) = (l-R)V2R.o. BaS04 was used as a reference. 

Further indications on the coordination of vanadium in the Vx-HMS series were obtained by wide line NMR spectroscopy. The results are summarized in Figure 6. In the dehydrated state, all samples show a broad signal at about -550 ppm characteristic of tetrahedrally coordinated V(V) species. An additional band is observed at c.a. -290 ppm for V3-HMS, which shows that this sample also contains octahedrally coordinated species, even in the dehydrated state. All samples very quickly rehydrate upon contact with air, which results in the appearance of a broad NMR signal at about -290 ppm.The process is completely reversible and the signal at 290 ppm disappears when samples are outgassed in vacuum at 250°C. 

From the wide line NMR powder spectrum of CS2TICI5 H2O. f From the wide line T1 NMR powder spectrum of NasTlClg I2H2O. 

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