Vibrational analysis and structural implications of H-bonding in isolated and aggregated 2-amino-1-propanol: a study by MI-IR and Raman spectroscopy and molecular orbital calculations

Isolated 2-amino-1-propanol (2AP) was studied by matrix-isolation infrared spectroscopy (MI-IR) in Ar and Kr and ab initio 6-31G* calculations undertaken at the HF-SCF and MP2 levels of theory. For the first time, five different conformational states of 2AP could be experimentally observed, which could be correlated with the most stable forms predicted by the calculations. The first and second lowest energy forms correspond to conformers which exhibit a considerably strong intramolecular OH ... N hydrogen bond (g'Gg' and gG'g), while the less abundant forms observed in the matrices (gGg', gGt and g/G'g) are characterized by having a weak intramolecular NH ... O or OH ... N bond. These results were reinforced by infrared solution studies of the compound in tetrachloromethane and tetrachloroethylene. The experimental data obtained for the pure liquid, where OH N intermolecular hydrogen bonding dominates, indicate that the preferred conformation of the monomeric unit within the aggregates is similar to conformer gGt. (C) 2000 Elsevier Science B.V. All rights reserved.