Molecular Spectroscopy Workbench: Interpreting Raman Spectra of Functionalized Polymers: Applying the Tricks of the Trade

摘要

In several of my earlier columns I discussed the interpretation of Raman spectra. This column continues that theme, examining the spectra of a series of functionalized celluloses. It is interesting to see what is consistent from material to material, and what is different. In particular, it is useful to identify marker bands for the various functional groups. In addition, when identifying an unknown, it is important to identify a collection of functional group bands that would all be present when that functional group is part of a molecule. Cellulose is a polymer of glucose whose functional unit has been recently identified as anhydrocellobiose, a glucose dimer with the beta-1,4 linkage between all glucose units (1,2). Actually, it has taken more than 30 years to understand the structure of cellulose by applying a combination of techniques, including chemical analysis, X-ray diffraction, electron diffraction, and nuclear magnetic resonance (NMR), Fourier transform infrared (FT-IR), and Raman spectroscopies. Because the symmetry of the cellulose molecule is quite low, prediction of vibrational group frequencies is not straightforward. As a result of systematic studies, however, the structure of the various crystalline forms of cellulose is now established and the Raman bands have been assigned.