Ultrasonic and spectroscopic studies on hydrogen bonded complexes of aromatic amine and aryl ketones in n-hexane at 303.15 K

Viscometric and ultrasonic studies have been carried out in n-hexane solutions, containing equimolar concentration from 0.02 to 0.2 M of aromatic ketones and N-methylaniline (NMANI), at 303.15 K and at atmospheric pressure. The ketones studied in the present investigation are acetophenone (ACP), 4-chloroacetophenone (ClACP) and 4-methylacetophenone (MACP). The behaviour of measured ultrasonic velocity (u), density (ρ) and viscosity (η) and also the computed acoustic parameters provide strong evidence for the presence of strong solute-solute interactions in the three ternary systems. Excess molar volume and excess thermo acoustic parameters reveal the existence of hydrogen bonded complexes between the solute molecules, ketones and secondary amine. The variation of these parameters with the concentration shows that the existing interactions are influenced by the structure of components and functional groups of the components involved. An attempt has been made to confirm the formation of 1:1 complexes in these systems through UV-visible spectroscopic method at 303.15 K. The calculated values of formation constants of the charge transfer complexes both by acoustic and optical methods agree satisfactorily. The variation in the values of formation constant reveals that electron releasing substituent in the acetophenone molecule enhances the stability while electronegative substituent decreases the stability of the complex. The negative values of free energy of formation of these three complexes indicate that these complexes are thermodynamically stable.