Calculated molecular properties for different alkanoic acid-alkylamine complexes: A comparison with measured FTIR and Raman spectra

In this work the charges, geometries, changes in geometries due to complexa tion, stabilization energies and vibrational frequencies have been calculat ed for three different propanoic acid (A)-propylamine (B) complexes. The co mplexes are A(3)B(1), A(1)B(3) and A(2)B(2) Furthermore, emphasis was given to clarifying which complex is the most stable one in binary solutions of alkanoic acid and alkylamine. The theoretically predicted vibrational spect ra are compared with IR and Raman spectra for the binary system heptanoic a cid-heptylamine. In theoretical calculations we have used Hartree-Fock and density function theory approximations. Calculations show the A3B1 complex to be the most stable one, which is also confirmed by the experiments at lo w amine concentrations. At equimolecular mixing ratios a A(2)B(2) complex s eems more likely. (C) 2001 Elsevier Science B.V. All rights reserved.