The acidity constants of the exhaustively substituted nitrosophenols with phenyl and ester substituents are determined. It was found that these compounds are more acidic than nitrosophenols with methyl groups, but less acidity than the persubstituted nitrosophenols with pyridine substituents. Quantum-chemical calculations, performed by the method of stationary density functional theory using exchange-correlation functional BP86 and def2-SVP basis set, have shown that the pyridine and nitrosophenol rings occupy an intermediate position between the orthogonal and coplanar functional. Thus, the hypothesis of a possible electron-withdrawing effect of the nitrogen atom of pyridine rings not only through the system of σ-bonds, but also due to the mesomeric effect through the residual coupling of π-systems is confirmed.