Infra-red studies and thermodynamics of hydrogen bonding in ethylene glycol monoalkyl ethers. Evidence for a ten membered ring dimer

Abstract

An i.r. study in the hydroxyl stretching region of three monoalkyl (methyl, ethyl and butyl) ethers of ethylene glycol in CCl4 solutions (concentrations up to 0.1 mol dm–3) has been carried out over the temperature range 298–338 K. Apparent integrated intensities of the bands at ∼3635, ∼3600 and ∼3475 cm–1 of the free, intramolecularly and intermolecularly bonded OH groups have been measured and used to evaluate the equilibria between the monomeric and associated species. Various possible structures including open and cyclic dimers, trimers and tetramers for the associated species absorbing at ∼3475 cm–1 have been considered. A cyclic ten-membered ring dimer involving the ether oxygens in hydrogen bonding satisfactorily explains the observed results. Various thermodynamic quantities such as K, ΔH°ΔG° and ΔS° in the three way equilibrium involving free monomer, intramolecularly bonded monomer and the cyclic ten membered ring dimer have been evaluated. The values of intra- and inter-molecular hydrogen bond strengths as calculated from the respective ΔH° values are ∼14.1 kJ mol–1 and ∼28.2 kJ mol–1 respectively.