Solvent dependence on conformational transition, dipole moment, and molecular geometry of 1,2-dichloroethane: insight from Car-Parrinello molecular dynamics calculations.

We have investigated the molecular geometry and dipole moment distribution for the major conformational states of 1,2-dichloroethane (DCE) in three different solvents under ambient conditions using the Car-Parrinello mixed quantum mechanics/molecular mechanics method. The solvents studied were water, DCE, and chloroform. Within the time scale investigated, we find a conformational equilibrium existing between the gauche and trans forms of DCE in all three solvents. In the chloroform solvent, the conformational transition occurs more frequently than in water solvent and in liquid DCE (i.e., DCE solute in DCE solvent). The population of gauche conformer is more in the case of water solvent, while the trans conformer dominates in chloroform solvent. We report a bimodal nature of the dipole moment distribution for DCE in all three solute-solvents studied, where the peaks are attributed to the trans and gauche conformational states. The dipole moments of both of the conformational states increase with increasing polarity of the solvent. Also, with an increase in solvent polarity, an increase in the C-Cl bond length and magnitude of atomic charges in DCE has been observed. The increase in atomic charges of DCE is almost twice when the solvent is changed from chloroform to water.