Nutation NMR spectroscopy

NMR properties, 33 213, 274 in nutation-NMR spectroscopy, 33 333 in sheer silicate smdies of, 33 340-341 layer structure, 32 184-186 on metal surfaces, 32 194-197 model, oscillatory reactions, 39 97-98 number... 

Of greater relevance catalytically is that the combined use of l3C enrichment and 13C nutation NMR spectroscopy can distinguish between proposed rival mechanisms for the Ziegler-Natta catalyzed polymerization of acetylene. In the four-center insertion mechanism the enriched acetylene (HC =C H) is incorporated as shown in Scheme 6. It is to be noted that the, 3C—13C bond label is here incorporated into a carbon-carbon double bond, the length of which is significantly smaller than that of a carbon-carbon single bond, which is how the enriched acetylene would be incorporated in the two-center mechanism shown in Scheme 7. The results of nutation experiments leave little doubt that the Ziegler-Natta polymerization of acetylene proceeds by a four-center mechanism. 

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... 

Solid state nutation NMR spectroscopy and X-ray diffraction, show that this ion has a trigonal structure with 1.46 and 2.51 A for central-methyl and C-C methyl-methyl distances (Fig. 8). 

Nutation NMR spectroscopy was introduced by Samoson and Lippmaa for the study of half-integer quadrupolar nuclei. For quadrupolar nuclei in the rotating frame, the nutation frequencies and amplitudes of the excited Zeeman... 

When intermediate regime) the evolution of the density matrix in the rotating-frame exhibits a much more complex behavior as function of the pulse length and this is the basis of the method known as nutation NMR spectroscopy [10,19]. The distinction between selective (ft>i -C coq), non-selective ([Pg.71]

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