The Dipole Moments of the Oligether of Ethylene Glycol

Abstract

The dipole moments of ethylene glycol dimethyl ether (N=1), diethylene glycol dimethyl ether (N=2), triethylene glycol dimethyl ether (N=3), and tetraethylene glycol dimethyl ether (N=4), were measured in n-hexane or benzene at 25°C and 45°C. The observed dipole moments of N=1, N=2, N=3, and N=4 are 1.59 D, 1.92 D, 2.16 D, and 2.44 D, respectively, in n-hexane at 25°C, 1.71 D, 1.97 D, 2.22 D, and 2.45 D, respectively, in benzene at 25°C, and 1.72 D, 1.98 D, 2.27 D, and 2.50 D, respectively, in benzene at 45°C. The dipole moments were theoretically calculated on the assumptions that: (i) the dipole moments of these chain molecules are given by the vector sum of the polar groups of ether whose group moment is 1.20 D, and (ii) all the internal rotations of a chain molecule are free. The calculated values of N=1, N=2, N=3, and N=4 are 1.67 D, 2.03 D, 2.33 D, and 2.60 D, respectively. The agreement between the observed and the calculated values is satisfactory. The solvent effect and the temperature dependence of the observed dipole moments have also been discussed in terms of chain flexibility.