CH2 rocking vibrations of polyethylene glycols

Abstract Measurements were made of the infrared absorptions of ethylene glycol and polyethylene glycols (from a dimer to a heptamer) in liquid state. In the case of polyethylene glycols, three distinct peaks appear in the wave number range of CH 2 rocking modes. This affords a conclusive evidence in support of the existence of the trans form as well as the gauche form of the O(CH 2 ) 2 O portion of linear chains. This confirms the result of dipole moment measurements that both gauche and trans forms are realized in the configurations of the lower members of polyethylene glycols in solution. Although it is reported that high molecular polyethylene glycol in crystalline state assumes a highly crumpled helical structure resulting from the gauche minima, the molecular structure of low molecular polyethylene glycols is not restricted to the same helical configuration. These chain molecules take a more or less irregular form resulting from the trans and gauche minima of the internal rotation about single bonds. Ethylene glycol shows only two absorption peaks in the wave number range of CH 2 rocking modes. A plausible explanation is presented based on the formation of intramolecular hydrogen bonds.