Cellulose carbon-13 signals

Figure 9 raises an Important question concerning crystalline polymorphy in the native celluloses. The hypothesis that higher plant celluloses like cotton and ramie are crystalline composites was suggested, in part, by the outer doublet and the sharper central feature of the Cl resonance in spectrum 9A. However, comparison of spectra 9A and 9C shows the central peak at Cl to be less intense at 200s compared with 1 ms, while the shape of the crystalline resonance at C4 remains constant. Since carbons C1-C5 relax at very nearly the same rates (32) in a T experiment, it is very likely that the signals for each of these carbons in... 

Typical CP/MAS C-NMR spectra recorded on isolated cellulose I are made up of four signal clusters originating from the six carbons in the anhydroglucose unit. The Cl cluster centered around lOS ppm, the C4 cluster centered around 87 ppm the C2, C3 and CS clusters centered around 73 ppm and the C6 cluster centered around 63 ppm. The fine structure of each signal cluster is due to the supermolecular structure of cellulose I. All chemical shifts reported here are determined by using glycine as an external standard. 

After carboxylation of cellulose by TEMPO mediated oxidation, the main observations corresponded to the appearance of the carboxyl groups signals near 175 ppm with the carboxyl peak at 1730 cm The NMR characterization of cellulose substrates indicated that oxidation is selectively realized on 06 carbons. 

---