Deuteron NMR spectra

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...

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. 

Record the proton and deuteron NMR spectra according to the directions of the instructor. The chemical shifts (relative to liquid tetramethylsilane) are -0.43 and -4.33 ppm for HCl and HBr, respectively, and a similar chemical-shift ordering is seen for DCl and DBr. Obtain expanded traces and integrate the peaks. Be consistent in choosing the integration limits the same ranges (abont five peak widths) shonld be nsed for all four peaks. Repeat the integration procednre several times to obtain an estimate of the nncer-tainty in the peak area ratios for H and D spectra. Record the sample probe temperatnre. 

Study the chain dynamics in the amorphous polymer atactic polypropylene. " The arrest of the structural relaxation above the glass-transition temperature Tg was investigated using ID and 2D deuteron NMR spectra. 

Fig. 2.1. Deuteron NMR spectra of selectively deuterated liquid crystal 8CB-ad2 at different temperatures.

Fig. 2.3. Deuteron NMR spectra of 5CB confined to untreated and lecithin-treated Anopore shown at several temperatures above Tni (from [19]).

Fig. 2.7. Deuteron NMR spectra 9 = 0, Troom) for various 5CB surface coverages A. The S doublets (gray frame), arising from the molecular deposition at the surface, exhibit a considerably smaller frequency splitting than the bulk doublets B (from [32]).

Deuteron NMR spectra provide particularly clear examples of the above approach. For deuterons ( H), the quadrupole interaction is by far dominant, and in a C-D bond is aligned with the C-D bond itself. Therefore, changes in time of the quadrupole... 

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. 

It will be useful to outline the basic features of solid state 2H NMR spectra. Deuteron is a spin 7= 1 nucleus possessing an electric quadrupole moment. The EFG interacts with the electric quadrupole moment to produce a frequency shift. Frequencies of the symmetric line shape centred around the Larmor frequency >0, which depend on the relative orientation of an external magnetic field B0 and the EFG tensor, are given by1 7... 

The NMR measurements were performed on systems composed of ca. 25 wt. % samples of aPS (M = 6.6x 10 g/mol, PD = 1.1, Pressure Chemical Company) in either reagent grade toluene (Aldrich) or toluene-d0 (Aldrich). The protonated solvent was used for the diffusion measurements and the deuterated solvent for the relaxation studies. At this concentration, the Tg j for the system was determined to be about -65 °C (i). The NMR spectra were run on a JEOL FX-90Q NMR spectrometer operating at 90 and 14 MHz for protons and deuterons, respectively. The T and T2 measurements were made with the standard inversion-recovery and spin-echo (CPMG) sequences, respectively. 

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... 

In case of a deuterated sample (spin 1 case), the spectra are usually dominated by the quadrupolar interaction, that is, the coupling of the nuclear quadrupole moment with the electric field gradient of the C-2H bond. For deuterons in C-2H bonds this can lead to a splitting of about 250 kHz. As in the case of dipolar interaction, a Pake spectrum is obtained for a powder sample. The z-principal axis of the quadrupolar interaction is oriented along the bond axis which makes deuteron NMR particularly useful for studies of segmental orientations and molecular dynamics (reorientation) [1],... 

Figure 3 2D O-D- O deuteron exchange NMR spectra of DRADA-32 at T= 40 K for fmix = 10 and 30 s. In addition to the diagonal peaks, the O-D- 0<->0- D-O exchange cross-peaks are clearly visible.

The ratios Po Jpoa and PBalPwr and hence K, are to be determined from the relative integrated peak areas of the deuteron and proton NMR spectra. A sensitive Fourier-transform NMR instrument with multinuclei capability is thus required, ideally at 200-MHz proton frequency or higher. Here we outline the essentials of a pulsed NMR experiment more detailed discussions can be found in Refs. 4 to 7. 

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