The Infrared Spectra of 2-Pyridone•••Ammonia and 2-Hydroxypyridine•••Ammonia Hydrogen-Bonded Complexes Interpreted by DFT Calculations and AIM Charge Densities

The optimized geometries and infrared spectra of the 2-pyridone•••ammonia and 2-hydroxypyridine•••ammonia hydrogen- bonded complexes were examined using the B3LYP/6-311++G(d,p) level of theory. By taking into account the tautomerism in the 2-pyridone and 2-hydroxypyridine molecules, the ammonia functions as donor and acceptor of proton in each hydrogen-bonded complex. Thereby, some classic aspects of hydrogen bonds can be observed, such as the redshift (bathochromic) effects in the N–H(ammonia), N–H(2-pyridone), and O–H(2-hydroxypyridine) bonds. In this insight, a theoretical investigation of these frequencies was performed not only by the B3LYP/6-311++G(d,p) calculations, but also by means of charge density integrations ruled by protocol of the theory of atoms in molecules (AIM), by which some molecular operators were computed, such as the electronic density centers (p) and Laplacian fields (v2p).