Conformations of some phenyl-substituted ethane derivatives as solutes

Abstract

The electric dipole moments of 1,2-diphenyltetrachloroethane and of three 2,3-di-(p-halogenophenyl)2,3-di-methylbutanes have been measured in carbon tetrachloride at temperatures from –20 to 45°. Molar Kerr constants and dipole moments in benzene are also reported for these compounds as well as the related molecules 1,1,2,2-tetrachloroethane, 1,1,2,2-tetrabromoethane, p-bromocumene, p-fluorocumene, and 2,3-dimethyl-2,3-diphenylbutane. Conformational analysis of the results shows that substitution of two phenyl groups for the hydrogen atoms in tetrachloroethane has little effect on the relative stabilities of the rotational isomers in solution. Substitution of p-halogenophenyl groups for the two Cl or Br atoms in 2,3-dihalogeno-2,3-dimethylbutane reduces (a) the ΔE(solution) value almost to zero, thereby altering the gauche : trans isomeric ratio; and (b) the dihedral angle θ from about 70 to 65°.