Infrared and Raman spectroscopy of carbohydrates. Part VI: Normal coordinate analysis of V‐amylose

A normal coordinate analysis of V‐amylose has been performed for an isolated 6 1 helical chain. Negligible splitting from interactions of vibrations of successive residues is expected between A and E vibrational species due to the large size of the monomer unit. As a result, calculation of only the totally symmetric A modes represents an adequate approximation to the vibrational spectrum of helical polysaccharides. Using this method together with a valence force field we have obtained good agreement between the observed and calculated frequencies. In addition, the computed potential energy distribution and Cartesian displacement coordinates match previous experimental assignments, based on deuterium exchange. The analysis also supports the proposed mechanism for conversion of V‐amylose to the more extended B‐form. This conversion results in an observed frequency shift for the Raman line at 946 cm −1 which is predicted by the calculations.