Host–guest complexes of phenol derivatives with β‐cyclodextrin: an experimental and theoretical investigation

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Abstractβ‐Cyclodextrin (β‐CD) is used as the host molecule to study the inclusion of a series of bent [bisphenol A (BPA) and fluorinated bisphenol A (FBPA)] or linear [biphenol (BIP) and isopropylphenol (IPP)] phenol derivatives. Experimental and theoretical investigations reveal that the complexes with the bent BPA and FBPA molecules are more stable than those with the linear IPP and BIP molecules. This stability difference is attributed to differences in the geometries which, in the case of bent molecules, seems to prevent the unthreading of the guest. The optimized geometry of the BIP/β‐CD complex shows a particularly strong deviation of the principal axis of BIP from the vertical symmetry axis (C7) of β‐CD. For bent molecules, the same sort of deviation is due to the second aromatic residue, which is outside the cavity, approaching the wider rim of the β‐CD, probably because of van der Waals interactions. In the FBPA/β‐CD system, experimental results (19F NMR) and DFT (MPWB1K//AM1) calculations demonstrate a different complexation mode from that of the three other systems, with high interaction energy, the phenol residues are located outside the β‐CD cavity but fluorinated alkyls are inside. This agreement indicates that MPWB1K/6‐31G(d) single point calculation based on AM1 geometries is a useful predictive tool for such series, even for systems as large as ours. Copyright © 2007 John Wiley & Sons, Ltd.