Intramolecular hydrogen bonding in ortho-aminomethylphenol is analysed with the aid of ab initio and density functional theory calculations. Selected properties of the components, phenol and benzylamine, are compared to those of the hydrogen-bonded form of the Mannich base as well as that of the non-hydrogen-bonded structure. Additionally, the gas phase infrared spectrum of benzylamine is analysed in terms of the possible conformations of the molecule. (C) 2000 Elsevier Science B.V.