The proton transfer and hydrogen bonding complexes of (2-hydroxyethyl)amines with acids: A theoretical study

The interaction of ethanolamines Me3-N(CH2CH2OH)(n) (n = 1-3) with arylheteroacetic acids Ar-Y-CH2COOH (Ar = 2-CH3C6H4, 4-ClC6H4; Y = O, S, SO2) as well as acetic acid itself has been studied. For isolated state, the geometries and electronic structures of the complexes obtained were calculated using OFT method at B3LYP/6-311+G** level of theory. The energy of the compounds has been calculated by means B3LYP/6-311+G** and MP2/6-311+G**//B3LYP/6-311+G** methods. It has been shown that proton transfer (PT) and hydrogen bonding (FIB) complexes are formed from triethanolamine (TEA) and the studied acids, while only HB complexes is generated from diethanolamine and ethanolamine derivatives. The TEA complexes are stabilized by N-H+center dot center dot center dot O- (PT) or O-H center dot center dot center dot N (HB) hydrogen bonds and O-H center dot center dot center dot O bonds of its hydroxyl groups and oxygen atoms of acid. The N-H+ center dot center dot center dot O- and O-H center dot center dot center dot N bonds in the complexes have a partial covalent character as predicted by the quantum theory of atoms in molecule (QTAIM). According to the second-perturbation energies E-(2) in the NBO scheme, highest charge transfer is along the O-H center dot center dot center dot N hydrogen bond for HB complexes of TEA with Ar-Y-CH2COOH. The GIAO calculated N-15 NMR chemical shifts are well correlated with NBO electron charges on the nitrogen atom for both type complexes. (C) 2012 Elsevier BM. All rights reserved.