SOLVENT EFFECTS ON 1,2-DIHALOETHANE GAUCHE/TRANS RATIOS

The effect of-solvent on the conformational equilibria for 1,2-dichloroethane and 1-chloro-2-fluoroethane was reinvestigated via IR spectroscopy and was examined theoretically via a new reaction field model. Cyclohexane solutions led to about one-third of the maximum solvent effect between the gas phase and a polar aprotic solvent. The G2(MP2) theoretical model led to trans/gauche energy differences in good agreement with the gas phase experimental data. The reaction field model, using the MP2/6-311+G** and Becke3LYP/6-311+G** theoretical levels, reproduced the experimental solvent effects, but the latter proved to be the more successful. Geometry optimization for a relatively high dielectric constant medium was carried out at the Becke3LYP level. The changes in structure and energy were relatively small.