Heteroassociation of Selected Diols with some Tertiary Amines

Abstract

AbstractDiols exhibiting the structure (HO)CH2–(CH2)n–CH2(OH) withn=1 up ton=4, (HO)CH2–CH(OH)–CH3and cyclohexan-1,2-diols as well as cyclohexan-1,4-diol, which may establish different intramolecular interactions, are used as model substances to describe the external hydrogen bonding behaviour of multivalent hydrogen bond donors in the presence of hydrogen bond acceptor molecules. In this study, hydrogen bonds formed by the diols with tertiary aromatic amines have been investigated. In solution, different associate formation between the diols and the acceptor molecules as sketched in Fig.1 may occur. Besides 1:1 associates formed by the interaction of one diol molecule with one amine molecule, 1:2 associates may be observed where each OH function interacts with one amine molecule. The equilibrium constants of the associates of those interactions have been studied by FTIR spectroscopy. The results allow a classification of the used diols in three different groups based on the position of the OH groups in the donor molecule. For diols with proton donating OH where no intramolecular hydrogen bond can be formed, the intermolecular hydrogen bonds for a 1:1 system may be described by thermodynamic parameters which are nearly twice the value of the corresponding equilibrium constants of monovalent alcohol systems due to the statistical weight of the OH groups. Secondly, when intramolecular hydrogen bond exists in the diols, the equilibrium constants in the interaction with the amine raise up by a factor ofca.2–3 due to the cooperativity effect. Thirdly, if the OH groups are arranged in 1,2 positions, both OH groups may be described as independent of each other in their intermolecular interaction with the amine.