Acidities of 1-indolylacetic and carbazolylacetic acids. Inductive constants of indolyl and carbazolyl groups

The pK_a values of 1-indolylacetic, 3-(9-ethyl)carbazolylacetic, and a number of 3,6-disubstituted 9-carbazolylacetic acids in aqueous ethanol solutions were determined by potentiometry.The inductive constants of the corresponding heterocyclic fragments were calculated from the values obtained. It is shown that annelation of the benzene ring with the pyrrole ring of indole gives rise to a decrease in the negative inductive effect of the heteroring. A linear relationship between the acidic properties of carbazoles and the corresponding 9-carbazolylacetic acids was established.