Signals monosaccharide, identification

Identification of constitutive monosaccharides two-dimensional homonuclear NMR techniques such as DQF-COSY and TOCSY are used to assign chemical-shift values for all C-bonded protons in each individual monosaccharide (96). One-dimensional NMR spectra provide useful information about the chemical shifts and scalar couplings of such well-resolved signals as methyl groups for 6-deoxy monosaccharides (fucose, quinovose, and rhamnose) at 6 1.1-1.3 ppm. 

Fourier-transform instruments, the two techniques are sufficiently different to be valuable complements to each other. In many cases, in particular when dealing with complex molecules, such as polysaccharides, the amount of information obtainable from H-n.m.r. spectra is limited, compared to that revealed3 by 13C-n.m.r. spectra. Monosaccharides may also yield H-n.m.r. spectra that are poorly resolved, even at high field, and that contain little information. On the other hand, proton-decoupled,, 3C-n.m.r. spectra are well resolved and, even if the signals are not assigned, a spectrum will provide an almost unambiguous identification of a compound. 

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