A molecular dynamics and Monte Carlo study of solvent effects on the conformational equilibrium of n -butane in CCl4a),b

We report on a computer simulation study of the gauche–trans conformational equilibrium of n-butane in liquid carbon tetrachloride solvent. The study is made possible by implementing an exact statistical mechanical theorem which relates the full intramolecular distribution function for a butane molecule to that of a hypothetical species which does not possess a large potential barrier separating the trans and gauche states. In addition to determining the trans–gauche equilibrium constant, the potential of mean torsion, that is, the reversible work required to alter the conformation is determined as a function of the dihedral angle. Recent theoretical work is compared with these computer experiments, and while qualitative agreement is found, the approximate theory overestimates the solvent effect. Finally, the change in solvent structure in response to a conformational change in the solute is determined.