SUBSTITUTED STYRENE MOLECULES INCLUDED IN CYCLODEXTRINS - A RAMAN-SPECTROSCOPIC STUDY .2.

Raman spectra of 3-bromostyrene, 3-nitrostyrene and 4-methoxystyrene ( 4MeOS) included in alpha-, beta- and gamma-cyclodextrins (alpha-, beta - and gamma CDs) were recorded. For the 3-substituted derivatives both the nu C=C and nu CH group wavenumbers were used for probing the gues t molecules, whereas for 4MeOS two pairs of bands in the 300-600 cm(-1 ) spectral region were analysed. On the whole, the spectral observatio ns suggest that the alpha CD inclusion leads, in all cases, to a confo rmational selection of the guest molecule, as previously reported for some other meta-substituted styrene molecules. On the other hand, the gamma CD complexation keeps approximately the conformer distribution o f the pure guest. In addition, temperature variation studies showed th at even below 200 K the conformer ratio remained unchanged, suggesting that the inclusion process in this CD hinders the internal rotation o f the vinyl group.