Spectroscopic and thermodynamic evidence of the auto-association of n-butylamine in open dimers and cyclic trimers

Abstract

The type of n-mers present in butylamine was evaluated. With density functional theory (DFT) techniques using the B3LYP functional combined with the 6-31G (d,p) basis set was found that the energetically more favorable structures are the open dimers and cyclic trimers. FT-Raman and FT-infrared spectra of pure Butylamine and n-Hexane, as well as of the binary system, were recorded to investigate the type and nature of the intermolecular complexes. The recorded FTIR and Raman spectra confirm the existence of these types of hydrogen-bonded complexes, making it possible to calculate the association constants and the heats of formation of both structures. These values are in the same order of magnitude than the results of thermodynamic determinations of other authors. In this way it was possible to correlate macroscopic and microscopic studies.