The Raman spectra of Valonia, which is approximately 65% I_α and Tunicate, which is almost all I_β are nearly identical, differing only in regions of cellulose spectra associated with hydrogen bonding or with the orientation of the methylene group at C6. Their similarities indicate that the conformations are nearly identical, and their structures differ only in patterns of hydrogen bonding. The keys to understanding the implications of the spectra are a number of normal coordinate analyses we have carried out. They included analyses, in sequence, of the series: the 1,5 anhydropentitols; the pentitols and erythritol; the pentoses; the hexoses; the inositols; cellobiose and the cello-oligodextrins. The core issue in all of their spectra is that the majority of their bands in the finger print and the low frequency regions are associated with vibrations of C-C or C-O bonds. For such bonds the reduced masses and bond energies are quite close, so in molecules consisting primarily of such bonds they are very highly coupled. Thus, differences in observed frequencies are primarily associated with differences in their geometry.

The near identity of the Raman spectra of celluloses I_α & I_β leaves little question that their skeletal geometries differ very little from each other. They differ significantly from the Raman spectra of highly crystalline native celluloses from other sources.

The observed Raman spectra of Valonia and Tunicate are much closer to each other than to the Raman spectra of any other celluloses. The Raman spectra of other forms of cellulose I will be presented and compared to those of Valonia and Tunicate. The conclusion arrived at is that the published structure of I_αis likely the closest approximation to the structures of both I_α & I_β. The accepted crystallographically based structure of the form I_β is not at all consisteent with the spectroscopic observations. The rationale for these conclusions will be presented.

Rajai Atalla

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