Influence of substituents on the ionization constant of benzimidazoles, benzotriazoles, indazoles, and indoles

Abstract

The influence of substituents on the pKa of benzotriazoles, 2-​(trifluoromethyl)​-​, 2-​(ethoxycarbonyl)​-​, and 2-​(methylthio)​benzimidazoles, 3-​chloroindazoles, indoles, and benzimidazoles, and of substituents in the 2-​position of 5-​chloro-​, 5-​nitro-​, and 4,​5,​6(or 7)​-​trichlorobenz-​imidazoles was detd. exptl. and by the Hammett equation pKa = ρΣσ + pKa0; σm was used for substituents in the 2-​, 4-​, and 7-​positions, and σp for substituents in the 5- and 6-​positions of benzimidazoles. The acidity of benzimidazoles was affected more by substituents in 2-​position than by substituents in the benzene ring.