Molecular structure, proton affinity and hydrogen bonds of (2-hydroxyethyl)amine-N-oxides: DFT, MP2 and FTIR study

Abstract

Tris- 1, bis- 2, and mono- 3 (2-hydroxyethyl)amine-N-oxides isomers, their protonated forms, and H-complexes with acids have been studied in gas phase and DMSO solution by the quantum chemical calculations using DFT and MP2 methods. It is found that the proton affinity of the endo isomers 1a–3a, exo isomers 1b–3b and epi isomer 1c depends on the number of the hydroxyethyl groups, steric factors and strengths of the intramolecular H-bonds OH⋅⋅⋅ON in 1a–3a and OH⋅⋅⋅OH in 1b–3b. The peculiarities of formation of the hydrogen bonded and proton transfer complexes of tris(2-hydroxyethyl)amine-N-oxide with trifluoroacetic and 2-methylphenyloxyacetic acids are defined by 1 configuration, acid strength and solvent polarity. The structure of 1 and its complexes upon transition to solution was determined using FTIR spectroscopy.