Molecular conformational equilibria in liquids

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Abstract
The extended RISM integral equation theory is employed to study molecular conformational equilibria in liquids. Solvent induced torsional free energysurfaces are computed for the solutes n‐butane and 1, 2‐dichloroethane at infinite dilution in apolar and polar model liquids, CCl4 and water. In addition, the intramolecular distribution of conformers for the neat molecular liquidsn‐butane and 1, 2‐dichloroethane are determined. The qualitative features of these free energies agree well with available simulation results. Quantitatively, the absolute solvent effects are consistently overestimated; however, the differences between polar and apolar systems are accurately predicted. The thermodynamic components of the solvent induced free energies for the dilute solutions are analyzed. For the systems examined here, the internal energy dominates the torsional free energies. In particular, for n‐butane in water, the increase in g a u c h e conformers is in accord with the notion of a hydrophobic interaction. However, the thermodynamic behavior found here opposes the usual belief that such association is an entropy driven process.