Abstract
Publisher Summary This chapter discusses the characterization of lignin by 1 H and 13 C nuclear magnetic resonance (NMR) spectroscopy. The latter includes techniques for obtaining routine, quantitative, and distortionless enhancement by polarization transfer (DEPT) 13 C NMR spectra of lignins. Among the various physical and chemical methods for characterization of lignins, 1 H NMR and 13 C NMR spectroscopy has been shown to be among the most reliable and comprehensive techniques. The characterization of lignin by 13 C NMR spectroscopy, in particular, furnishes rather comprehensive data about the nature of all carbons in lignin in terms of chemical structure. By contrast, the other physical and chemical analytical methods only provide incomplete information on the chemical structure of lignin. However, several difficulties are still encountered in the interpretation of the 1 H NMR and 13 C NMR spectra of lignins—for example, the assignment of signals, because of the intensive overlap of signals for 1 H and 13 C nuclei in lignin present in similar, but nonidentical chemical environments. Some of these difficulties can be circumvented by the application of more sophisticated 13 C NMR pulse sequences such as the attached proton test experiment and the DEPT sequence.
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