| Abstract
| - Intramolecular hydrogen bonds influence intermolecular binding in adsorption and molecular recognition,but the interplay between intra- and intermolecular hydrogen bonding is poorly understood. In this study, aseries of four aromatic alcohols, 2-phenylethanol, 3-phenyl-1-propanol, 2-phenoxyethanol, and 3-phenoxy-1-propanol, are examined to determine the effect of intramolecular hydrogen bond formation on the bindingto ethyl propionate (EP), an analogue of an acrylic ester separation resin. A combination of infraredspectroscopy, molecular modeling, and ab initio calculations are used to investigate the conformationalpreferences of the alcohols and the alcohol:EP complexes in hexane. Without EP, 2-phenylethanol and2-phenoxyethanol prefer intramolecularly hydrogen-bonded conformations, whereas 3-phenyl-1-propanoloverwhelmingly favors a conformer without an intramolecular hydrogen bond. For 3-phenoxy-1-propanol,there is a smaller preference for conformers without an intramolecular hydrogen bond. These results agreequalitatively with the experimentally measured IR spectra. The conformational preferences are explained byexamining the energy components of low-energy conformers. Electrostatic interactions favor the intramolecularly hydrogen-bonded species, whereas the dihedral energy term and entropic term favor conformerswithout an intramolecular hydrogen bond. The balance determines the most stable conformer. The calculationspredict that all four alcohols bind EP weakly compared with para-methoxyphenol. This ranking is in goodagreement with experimental adsorption measurements. The small calculated ΔG° values of ≈ −0.9 to −2.4kJ/mol for the alcohols is explained in terms of hydrogen bond donating ability, entropy, and the competitionbetween inter- and intramolecular hydrogen bonds.
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