Theoretical studies on ethanolamine in gas phase and solution: Conformations, frequencies and basicities

__________________ Abstract _____________________________________________________________________ The conformational stability, intramolecular H-bond strength, energy barriers, vibrational frequencies and gas-phase basicities of fourteen most stable conformers of ethanolamine in gas phase and in aqueous and carbon tetrachloride solutions have been investigated at B3LYP and MP2 level with 6-311+G(d,p) basis set. In gas phase, the results of two methods suggest that G1 and G2 conformers, which possess intramolecular H-bonds, are the two most stable conformers. The population ratios of T-, Gand G-type conformers are about 2.2%:48.9%:48.9% (B3LYP), 1.2%:49.4%:49.4% (MP2). The energy barrier of interconversions G5 → T1 is obviously larger than that of T2 → T3. In aqueous solution (SCRF-PCM method), the calculations indicate that the stabilizations of ethanolamine conformations are determined by the combination of intramolecular hydrogen bonds and intermolecular solvation of hydroxyl groups. The normal mode analysis for vibrational frequencies shows that the C-O-H bending and the C-O stretching frequencies of the conformers from high energy to low energy are blue-shifted, the O-H stretching frequency is red-shifted conversely. The computed vibrational frequencies in carbon tetrachloride solution are in good agreement with the experimental data. The calculated results of gas-phase basicities of different ethanolamine conformers suggest that the GBs of G-type conformers are higher than that of T-type conformers. ______________________________________________________________________