BETA-CYCLODEXTRIN COMPLEXES OF BENZALDEHYDE, VANILLIN AND CINNAMALDEHYDE - A RAMAN-SPECTROSCOPIC STUDY

Raman spectra of benzaldehyde, vanillin and trans-cinnamaldehyde, and of their complexes in beta-cyclodextrin are presented and discussed. T he guest molecules provide both an aromatic ring for privileged intera ction with the cyclodextrin cavity, and characteristic vibrations (e.g ., nu C=O, nu C=C, nu CCphi (phi=phenyl), nu C-H-phi) with group frequ encies in spectral regions free from cyclodextrin bands which are usef ul for probing the guest perturbed by complex formation with beta-cycl odextrin. In particular, the C=O bond is shown to be a good vibrationa l spectroscopic probe to monitor the effects of both the medium, throu gh its dielectric constant, and of specific interactions, namely of th e hydrogen bonding type. The first of these effects is evaluated theor etically and a Kirkwood-Bauer-Magat plot for benzaldehyde is used to e stimate the effective dielectric constant for the guest in the benzald ehyde-beta-cyclodextrin complex. The above mentioned Raman spectroscop ic results ate interpreted and discussed.