Deuteron NMR

By using a selective deuteration, H NMR allows investigation of motions of specific groups within a polymer chain. 

At temperatures higher than - 70 °C, the methyl deuteron fine shape corresponds to rapid rotation of the methyl group. This rotation in the rapid exchange limit leads to an averaged field gradient tensor, whose principal axis is along the spatially fixed C - CH3 bond direction. As there is not any 

In order to investigate the phenyl ring motions by NMR, deuterated phenyl BPA-PC (BPA-d4-PC) has been prepared by deuteron substitution in ortho position to the carbonate link, and studied in the temperature range from - 110 to 120 °C [36]. 

In the temperature range below room temperature, the fully relaxed and partially relaxed NMR spectra [36] are shown in Fig. 41. Whereas at - 113 °C the fully relaxed spectrum only shows a rigid Pake doublet, at higher temperatures the line shapes can be considered as a superposition of spectra in the rigid and rapid exchange limit with a weighting dependent on temperature. The simulated spectra (Fig. 41) have been calculated by consid- 

For describing this heterogeneous distribution of jump rates, a symmetric log-Gaussian distribution is not satisfactory, as mentioned. An asymmetric distribution with a more rapid decay at low rates, similar to the Williams-Watts distribution, yields an excellent agreement with the experimental data. 

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Deuteron NMR — A new Tool for Studying Chain Mobility and Orientation in Polymers... 

Pulsed deuteron NMR is described, which has recently been developed to become a powerftd tool for studying molectdar order and dynamics in solid polymers. In drawn fibres the complete orientational distribution function for the polymer chains can be determined from the analysis of deuteron NMR line shapes. By analyzing the line shapes of 2H absorption spectra and spectra obtained via solid echo and spin alignment, respectively, both type and timescale of rotational motions can be determined over an extraordinary wide range of characteristic frequencies, approximately 10 MHz to 1 Hz. In addition, motional heterogeneities can be detected and the resulting distribution of correlation times can directly be determined. 

Fig. 21. Deuteron NMR spectra for the phenyl groups in polycarbonate (amorphous film, drawn from solution at room temperature, Mw 30000, Mw/M = 1 -8). Left column fully relaxed spectra. Right column partially relaxed spectra corresponding to the mobile groups only...

Fig. 22. Deuteron NMR spectra at room temperature for the phenyl groups in polycarbonate itself and in mixtures of polycarbonate and para-dichlorobenzene and polychlorinated biphenyls as indicated. Note that the additives block the phenyl motion for a substantial fraction of the monomer units...

Komfield J.A., Spiess H.W., Nefzger H., Hayen H., and Eisenbach C.D. Deuteron NMR measurement of order and mobility in the hard segments of a model polyurethane, Macromolecules, 24, 4787, 1991. Meltzer A.D., Spiess H.W., Eisenbach C.D., and Hayen H. Motional behaviour within the hard domain of segmented polyurethane A NMR study of a triblock model system. Macromolecules, 25, 993, 1992. 

Proton NMR and deuteron NMR spectra of soluble fractions and spent solvent mixtures were obtained by using a JE0L FX60Q FT NMR Spectrometer. A flip angle of 45° was used which corresponds to 14 ms for and 75 ms for 2H. The pulse repetition times were 6.0 and 9.0 s, respectively. Chloroform-d was used as the NMR solvent, and chloroform was used as the 2H NMR solvent. 

Translation and reorientation of CD4 molecules in zeolites as studied by deuteron NMR relaxation... 

Keywords deuteron NMR, free rotator CD4, molecular dynamics, zeolite NaY. 

Nuclear magnetic resonance provides means to study molecular dynamics in every state of matter. When going from solid state over liquids to gases, besides mole- cular reorientations, translational diffusion occurs as well. CD4 molecule inserted into a zeolite supercage provides a new specific model system for studies of rotational and translational dynamics by deuteron NMR. 

For a 60-MHz instrument, the proton NMR spectrum of HD shows lines separated by 43.5 Hz. (a) Give the number of lines and their relative intensities in the HD proton NMR spectrum, (b) Give the number of lines, their relative intensities, and their spacing for the HD deuteron NMR spectrum, (c) Calculate the proton-proton coupling constant in H2. 

Deuteron -NMR measurements on the same system (labelled in the methyl group) also show that the mobility of the hydrophilic ammonium head group is reduced by... 

For an oriented sample with a uniform director orientation the 23Na NMR spectrum at a weak radiofrequency field thus consists of three equally spaced peaks. The relative magnitude of the three resonance lines is governed by the transition probabilities between the different energy levels. It turns out (9) that the central line contributes 40% of the total intensity while each of the satellites contributes 30%. The deuteron NMR spectrum consists of two equally intense peaks. 

The appearance of a sharp central peak in the deuteron NMR spectrum for unaligned lyotropic liquid crystalline samples has been observed by several authors (30, 33, 34). This has been interpreted in terms of phase inhomogenities (35) or isotropic motion (36). However, recently Wennerstrom et al. showed for a lamellar amphiphile-water mesophase that this could be referred to double quantum transitions (37). It is expected that double quantum transition peaks appear in NMR spectra... 

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