Infrared spectra and rotational isomerism of mono-, di-, and tri-ethylene glycol monoalkyl ethers

Abstract

Infrared spectra have been recorded of the following mono-, di-, and tri-ethylene glycol monoalkyl ethers: C_nH_2n+1OCH₂CH₂OH where n = 17 and 19; C_nH_2n+1(OCH₂CH₂)₂OH where n = 17, 18, 19, and 22; and C₁₈H₃₇(OCH₂CH₂)₃OH. Spectra of the pure liquids, solutions in CCl₄, and the solids at room and liquid air temperatures have been studied. From a study of the CH₂ rocking modes at 927-934, 889, 900, and 862 cm^-1 during the liquid-solid transformation and from solution studies, it has been shown that both the OCH₂CH₂O groups in diethylene glycol monoalkyl ethers exist predominantly in the gauche conformation in liquid and in solution. However, in the solid, while the end OCH₂CH₂O group takes both trans and gauche forms, the OCH₂CH₂O group adjacent to the polymethylene chain appears to take a trans configuration. The long polymethylene chain is found to pack in a triclinic subcell in the solid state, while in the quenched liquid state an orthorhombic or monoclinic packing is indicated. The present investigation has led to the conclusion that the difference in the conformations of end CH₂CH₂CH₂OH groups found between the odd and even chain n-alcohols is removed in mono- and diethylene glycol monoalkyl ethers by the introduction of one or two OCH₂CH₂ groups.