An experimental and theoretical study of the acid-base properties of substituted indoles.

Abstract

Experimental and theoretical studies on the acidity and basicity of a representative set of benzene substituted indoles have been carried out. Aqueous ionization data, obtained spectrophotometrically at 25°C, were comparatively analyzed by the Hammett Acidity function and the Excess Acidity methods. Ionization constants, pKas and solvation m * parameters are reported. Gas-phase ionization enthalpies have been theoretically calculated using the AM1 semiempirical method. Single and double parameter relationships between the theoretical and experimental ionization data and the Hammett substituent constants are observed.