Correlation of Dissociation Constants of 2- and 2,6-Substituted Anilines in Water by Methods Based on the Similarity Principle and Quantum-Chemistry Calculations

Abstract

In the context of studies of the ortho effect, two series of 2-monosubstituted (H, CH3, CF3, OH, CH3O, F, Cl, NH2, CN, NO2) and 2,6-disubstituted anilines (containing all combinations of CH3, CH3O, Cl, and NO2 substituents) were chosen for this work. Commercially unavailable derivatives were synthesized, and dissociation constants in water were determined for those substances for which the proper measurements had not yet been carried out. A critical compilation of pKa literature data has been summarized and compared with the authors' own data. The analysis and interpretation of the ortho substitution effect and its manifestation in the dissociation constants of the studied anilines (as log Ka) was based on two different approachescorrelation analysis (similarity principle) and quantum-chemistry calculations. The classical correlation equation with substituent constants σI and σR was extended by the parameter υ describing the steric effects, but the correlation was not close enough (s = 0.514, R = 0.986). ...