β-Cyclodextrin Complexes of Benzaldehyde, Vanillin and Cinnamaldehyde: A Raman Spectroscopic Study¹

Abstract

Raman spectra of benzaldehyde, vanillin and trans-cinnamaldehyde, and of their complexes in β-cyclodextrin are presented and discussed. The guest molecules provide both an aromatic ring for privileged interaction with the cyclodextrin cavity, and characteristic vibrations (e.g., vC=O, vC=C, vCCϕ (ϕ=phenyl), vC-Hϕ) with group frequencies in spectral regions free from cyclodextrin bands which are useful for probing the guest perturbed by complex formation with β-cyclodextrin. In particular, the C=O bond is shown to be a good vibrational spectroscopic probe to monitor the effects of both the medium, through its dielectric constant, and of specific interactions, namely of the hydrogen bonding type. The first of these effects is evaluated theoretically and a Kirkwood-Bauer-Magat plot for benzaldehyde is used to estimate the effective dielectric constant for the guest in the benzaldehyde-β-cyclodextrin complex. The above mentioned Raman spectroscopic results are interpreted and discussed.