Solvent and Substituent Effects on the Spectra of Some Substituted Thioureas

Abstract

AbstractA study on the effect of a number of solvents, covering a broad polarity range i.e. from dioxane (D=2.20) to acetonitrile (D=38.0), has been made on the electronic transitions of N‐aryl, N′‐2‐(5‐halo‐pyridyl) thioureas (where aryl= ‐C2H5 or O‐CH3‐C6H5‐, and halo= ‐Cl, ‐Brand ‐I). Two intense absorption maxima in the regions 270‐285 nm (assigned for thiocarbonyl π‐π* transition) are exhibited by all the substituted thioureas studied. The excitation energies and oscillator strengths of these transitions have been calculated. A correlation between ‘ET’ and ‘Z’ (an empirical measure of solvent polarity) has been attempted. Solvent sensitivities of these compounds have also been calculated.The effect of halo‐substituents, in the pyridine ring, on the spectra of these substituted thioureas has also been studied. It has been proposed that there is a delocalization of electrons between the pyridine ring and the thiourea unit of these compounds. This delocalization of electronic charge is affected by the substitution of the halo‐groups in the pyridine ring at para position to the thiourea unit which is reflected in the intensities and shifting of the absorption maxima.