SOLUTE-SOLVENT INTERACTIONS .4. INFRARED STUDIES OF SOLVENT EFFECTS ON ROTATIONAL ISOMERS OF 1,2-DICHLOROETHANE AND 1,1,2,2-TETRACHLOROETHANE

The influence of solvents on the C-Cl stretching absorption bands of the trans and gauche isomers of 1,2-dichloroethane and 1,1,2,2-tetrachloroethane was examined in terms of both relative frequency shifts and relative band intensities. The results indicate that the interaction of 1,2-dichloroethane with the solvents studied is mainly dielectric in nature. However, with 1,1,2,2-tetrachloroethane hydrogen bonding also becomes significant in proton-acceptor solvents, and it occurs with both isomers. A reasonably linear relationship exists between the relative intensities of the C-C1 stretching bands of the rotational isomers of each of these two solutes and the relative frequency shifts of the C-C1 stretching bands of n-propyl chloride or isobutyl chloride. This fact and also other evidence suggests that the main interaction responsible for the variation in relative stability of the two isomers in different solvents is dielectric in nature, and that the contribution of hydrogen bonding is less significant. It s speculated that the anomalous stabilization of the gauche isomer observed in aromatic solvents also is caused by an electrostatic rather than a hydrogen-bonding interaction. © 1969, American Chemical Society. All rights reserved.