13C-N.m.r. spectroscopy

Natural-abundance, 13C-n.m.r. spectroscopy is not a technique that may be applicable to all systems. It does have a few drawbacks, despite its overall, positive appeal. The relatively low gyromagnetic ratio of carbon-13, its low sensitivity, and its low natural abundance do present some handicaps.33 However, these factors are outweighed by the large chemical-shift range for carbon atoms in glycoproteins (—200 p.p.m.) and the fact that glycoproteins contain a multitude of carbon atoms... 

II. General Considerations Concerning Glycopeptide Structure Classical Methods for Ougosaccharide Structural Elucidation, and the Use of 13C-N.m.r. Spectroscopy... 

VI. Summary of the Application of 13C-N.m.r. Spectroscopy to the Study of Glycoproteins, and Possible Future Uses... 

The possible occurrence of such major rearrangement of a compound s carbon skeleton, during the course of apparently unequivocal reactions, is clearly of the utmost significance in interpreting the results of experiments aimed at structure elucidation particularly when the actual product is isomeric with the expected one. Some rearrangements of this type are highly complex, e.g. in the field of natural products such as terpenes, and have often made the unambiguous elucidation of reaction pathways extremely difficult. The structure of reaction products should never be assumed but always confirmed as a routine measure lH and 13C n.m.r. spectroscopy have proved of enormous value in this respect. 

Tautomerism both in the solid state and in solution is confirmed by infrared spectroscopic measurements on all three compounds [54,55]. The highest content of ketohydrazone form within the three isomeric phenylazonaphthols occurs, in solution, with 2-phenylazo-l-naphthol [56]. A 15N-n.m.r. study of some azo dyes derived from H acid and related intermediates has confirmed the dominance of the ketohydrazone tautomer [57]. Similar findings have been obtained using high-field H- and 13C-n.m.r. spectroscopy [58]. 

The advent of studies of polysaccharides by carbon-13 nuclear magnetic resonance (13C-n.m.r.) spectroscopy coincided, not surprisingly,... 

C-n.m.r. spectroscopy is useful in monitoring the purity of polysaccharide preparations. Similarly, in a multicomponent, biological system, such as exists in fungal cell-walls, the varying proportion of each polysaccharide can be gauged, once characteristic signals have been identified. 

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