Infrared study and thermodynamics of hydrogen bonding in diethylene glycol monoalkyl ethers
Abstract
Diethylene glycol monoalkyl ethers in dilute CCl4 solutions exhibit three OH bands, viz. at ∼3635, ∼3600 and ∼3475 cm–1 attributable to a free monomer (MF), an intramolecularly hydrogen bonded five-membered ring monomer (M5) and an intramolecularly hydrogen bonded eight-membered ring monomer (M8) respectively. In concentrated solutions, the dimer (D) band appears at ∼3440 cm–1. The relative concentrations of these species involved in the multiple equilibria are observed to be in the order CD≈CFC8≈½C5 at 298 K. The thermodynamic quantities for the equilibria M5⇌ MF, M8⇌ MF and D ⇌ 2MF are ΔH°5F∼ 12 kJ mol–1, ΔS°5F∼ 22 J K–1 mol–1; ΔH°8F∼ 21 kJ mol–1, ΔS°8F∼ 56 J K–1 mol–1 and ΔH°DF∼ 58 kJ mol–1, ΔS°DF∼ 153 J K–1 mol–1 respectively. Finally a ten membered ring, involving the OH group of one molecule bonded to the β-oxygen of the other molecule, similar to that in alkoxy ethanols is found to be the most likely structure for the dimer.