Calculated and measured vibrational frequencies in an alkanoic acid-alkylamine complex

Calculated geometries, charges and harmonic frequencies have bean obtained for a complex consisting of propanoic acid and propylamine in a molecular r atio of 3:1 using ab initio quantum-chemical methods. The calculated harmon ic frequencies are compared with a Fourier transform infrared spectrum for a binary mixture of heptanoic acid and heptylamine in a molecular ratio of 3.1. Except for the oxygen-hydrogen stretching vibration in the hydroxyl gr oup of the unionized acids, there is a good correlation between the calcula ted and measured frequencies. (C) 2000 Elsevier Science B.V. All rights res erved.