Hydration of the Oxyethylene Chain. Hypersonic Velocities in Aqueous Solutions of α-Methyl-ω-methoxyoligo(oxyethylene)s and α-Methyl-ω-hydroxyoligo(oxyethylene)s as Studied by Brillouin Scattering

Abstract

Abstract Hydration of the oxyethylene chain was studied by a Brillouin-scattering method; hypersonic velocities in aqueous solutions of CH3(OCH2CH2)mOCH3 with m=1–4 and CH3(OCH2CH2)mOH with m=2 and 3 were measured. The concentration of the solution, at which the sound velocity gave a maximum value, led to the number of water molecules, at the highest hydration, per ether linkage in the oxyethylene chain. The experimental results showed that 1.8 water molecules take part in the hydration of each –CH2OCH2– group and that the number of the water molecules is virtually constant independently of the oxyethylene-chain length as far as the number of the oxyethylene units is limited up to four. These findings indicate that a sort of hydration complex of approximately 1 –OCH2CH2–:2 H2O is formed in the aqueous solution. It is suggested that the stabilization of the gauche conformation for the OCH2–CH2O group in aqueous solution, as evidenced by Raman-spectroscopic observations, is promoted greatly by the hydrogen bond of water molecules which are bridged between the adjacent ether oxygens in the oxyethylene chain.