[xilus1]

I need some help with this question:

Why do the cyclic oligosaccharides alpha-, beta- and gamma-cyclodextrin exhibit an identical number of Raman-active vibrational coordinates? How would their measured Raman spectra look when compared?

I don't really know where to start. I know that a,b, g -CD belong to the C6, C7 and C8 point groups respectively and that they share the same raman-active modes (indicated by the quadratic functions in the character table) but I can't rationalize it.

Any help would be much appreciated. Thanks

[Corribus]

Big molecules - most of their vibrational modes will be localized, such that the overall molecular symmetry won't matter a whole lot. Apparently there are delocalized ring modes as well. Since the symmetry classes are more or less identical, the activity of those modes across the series should also be more or less identical. I would expect the energy of that vibration to change slightly as the ring size is increased, but apparently the difference is not large.

As to what the spectra look like, here you go:
https://www.sciencedirect.com/science/article/pii/S0957416600805376

[xilus1]

Thank you very much! I'm on the right track now and that paper was very helpful.