Hydrogen Bonding in Monomers and Dimers of 2-Aminoethanol

Abstract

Equilibrium structures of monomers and dimers of 2-aminoethanol (AE) exhibiting different intramolecular and intermolecular hydrogen bonds between the OH and NH 2 groups were optimized and analyzed in theoretical density functional B3LYP/6-311++G(2d,2p) calculations. Natural bond orbital (NBO) theory was applied to quantify the relative strength of these interactions and to account for their effect on stability, structural, and vibrational parameters of both monomers and dimers. It is shown that the charge transferred from the lone pair of the hydrogen bond acceptor to the antibonding orbital of the donor provides the substantial stabilizing component of the hydrogen bond. NBO energetic analysis demonstrates that the OH···N interaction is the strongest one for both monomers (intramolecular) and dimers (intermolecular). The intramolecular hydrogen bond in AE monomers is relatively weak, in part, because of its bent nature. The formation of a stronger and more linear intermolecular hydrogen bond between molecular units in AE dimers is accompanied by cooperative enhancement of the intramolecular hydrogen-bonding interactions. This effect is explained in terms of charge transfer among local bond orbitals and is relevant to the cooperative strengthening of hydrogen-bonding interactions in larger AE clusters.