Proton nutation

Lyerla et al. measured Tic over a wide temperature range from room temperature down to 105 K [94], and concluded that Tic s of not only CH3 but also CH resonances depend on CH3 rotational motion, and that the broadening of the CH3 resonance below -100 °C is also due to modulation of CH3 rotational motion at the frequency of proton nutation in the presence of the decoupling field. Gomez et al. have also reported solid-state high-resolution 13C NMR spectra of isotactic polypropylenes [95]. They used samples characterized by X-ray crystallography and reconfirmed the results obtained by Bunn et al. 

The shape selectivity of zeolites is influenced by the location and distribution of charge-compensating cations. The charge-compensating ions other than protons are all quadrupolar. and Li NMR spectra of dehydrated LiX-1.0 identified three crystallographically distinct sites [221]. In the case NaX with Si/Al ratio of 1.23, six distinct sodium sites were identified using fast Na NMR, DOR and nutation techniques [222]. Na MQMAS has been extensively studied for zeolites X and Y [155]. Other cations like Cs and La in zeolites have also been investigated [155,... 

The angle dependence of the spin soliton in randomly oriented ladder poly-diactylene has also been investigated79 by pulsed HFEPR at 94 GHz. The shape of the 0-anisotropy-resolved nutation spectrum was discussed on the basis of the EPR transition moments and the differences between spin relaxation times. Reliable assignments of hyperfine couplings to the p-protons (P-H) of the alkyl side chains were achieved with the support of W-band ENDOR measurements. No significant orientational dependence of the 7i and Ti processes was found in terms of the isotropy of the p-H-hyperfine interaction. 

The disordered nature of the amorphous phase has prevented the direct determination of the structural parameters by the usual structural techniques such as X-ray diffraction. Solid-state NMR can give us those parameters even for amorphous samples. Yannoni and Clark [14] applied nutation NMR spectroscopy, which is specifically designed to measure interatomic distances, to determine the bond lengths in both the cis- and tran -polyacetylenes. They used polyacetylene polymerized from a mixture of 4% doubly C-enriched acetylene and doubly depleted acetylene. In Fig. 7.6, the observed and simulated proton decoupled nutation spectra of the cis sample are shown. The sharp peak in the centre arises from the isolated nuclei in the sample. The remainder of the spectrum is a Pake-doublet arising from the dipolar coupling of adjacent nuclei in the polyacetylene. The best fit to the observed spectrum corresponds to a distribution of bond length with... 

The method is most appropriate when the spectmm is dominated by a single resonance, so has obvious application to samples in heavily protonated water but can be equally effective fcff organic solutions when a single dominant peak can be identified, such as a resolved methyl resonance for example. This must be placed on-resonance, and the smallest frequency separation between the anti-phase peaks in the nutation spectmm is then used in the appropriate calculation. The whole procedure is most conveniently executed through appropriate software routines, which may be supplied as standard by your instrument vendor. 

Nuclear Magnetic Resonance (NMR) methods have somewhat limited application to CPs, due to requirements for solubility or constraints magic angle spinning (MAS) or other adaptations to solid-state methods. Proton and C solution NMR are of course confined to the soluble, de-doped forms of CPs, in solvents such as CDCI3, and deuterated dimethyl formamide. Solid state methods have been applied with some success primarily to P(Ac). And nutation NMR studies have yielded some useful bond length information. Besides the illustrative studies cited below, many studies using NMR of CPs in conjunction with other analytic techniques for structural elucidation abound [410, 439, 440]. 

Fig. 28. Proton spin-lattice relaxation times in the laboratory system (Tj) and in the rotating frame (Tip) of polyisobutylene (PIB) melts as a function of the frequency (v, Lar-mor frequency in the laboratory frame Vi=yBi/(27i), rotating-frame nutation frequency) [125]. The data refer to the molecular weight independent chain-mode regimes I (high-mode-number limit) and II (low-mode-number limit) [49], The arrow indicates the crossover frequency between regions I and II...

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