Abstract

MEJIA, Sol M; ESPINAL, Juan F  and  MONDRAGON, Fanor. COOPERATIVE EFFECTS IN (ETHANOL)3-WATER HETEROTETRAMERS. Rev.Colomb.Quim. [online]. 2009, vol.38, n.1, pp.151-167. ISSN 0120-2804.

Density Functional Theory (DFT: B3LYP/6-31 + G(d)) was used for the optimization of clusters on the potential energy surface of (ethanol)3-water heterotetramers. The tetramerization energies can reach values up to -21.00 kcal/ mol. This energy can not be obtained by just considering the contributions from interactions between two cluster molecules, which suggests of the presence of global cooperative effects (positive). These effects are reflected in smaller hydrogen bond distances and smaller oxygen-oxygen distances, as well as in greater elongations of the O-H proton donor bond with a stronger "red-shift" in the heterotetramers compared to the ethanol-water heterodimers and the ethanol dimer. The largest cooperativity effect was observed in the four hydrogen bonds arranged in the largest possible cyclic geometric pattern, where all the molecules act as proton acceptor and donor simultaneously. A similar analysis to the characterization of (ethanol)3-water heterotetramers was carried out on (methanol)3-water heterotetramers, and ethanol and methanol tetramers, whose comparison showed a great similarity between all evaluated parameters for the clusters with equal geometric pattern.

Keywords : hydrogen bonds; cooperative effects; ethanol-water azeotrope; proton donor-acceptor systems; molecular modeling.

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