ELECTRONIC AND VIBRATIONAL ABSORPTION SPECTRAL STUDY OF SOME N - SUBSTITUTED ANILIDES AND SULPHONANLIDES

ABSTRACT 

The electronic and vibrational absorption spectra of some N - substituted anilides and sulphonanilides have been studied. The different bands observed have been assigned to the proper electronic and vibrational transitions respectively. The solvent dependence of n - n* and n- n* transitions in these compounds was investigated by studying their UV spectra in pure organic solvents of different polarities. The longest wavelength band displayed by the anilides and the sulphonanilide in carbon tetrachloride and methanol is assigned to both intramolecular and intermolecular charge transfer transitions, CT. This band exhibits an appreciable red shift in its Ama'< with increase in solvent polarity, a behaviour that indicate that the excited states of these compmmds are more polar than their ground states. The red shift can be ascribed to the stabilization of the polar excited states as the solvent polarity increased. The Infrared absorption spectra of the anilides were characterized primarily by the three backbone Infrared bands of amide I, amide II and the N -H stretching vibrations in all the compounds. The sulphonanilides on the other hand exhibited both S=O and N-H stretching vibrations also characteristic of the group. The results showed an increase in the carbonyl absorption frequencies as the electron-attracting ability of the p-substituent increased. The highest absorption values were recorded for the bromo-derivatives owing to strong inductive effect. A similar trend was observed for the sulphonyl vibration, S=O. Quantitative assessment of the electronic effect transmission in both groups of compounds was carried out by subjecting the data obtained to correlation analysis via the Hammett plots of V c=o and Vs=o against 8p respectively for the anilides and the sulphonanilides. The result is a measure of the susceptibility of their reaction centers to changes in electron density as caused by various substituents.