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Quantum chemical calculations using DFT (B3LYP and PBE0) and MP2 approximations with ccpVTZ basis sets have been performed for 10 N-oxides with different substituents. The influence of the substituent nature on the geometry and redox properties of the compound, as well as on the parameters of the semipolar N ? O bond, has been analyzed. The presence of strong electron-withdrawing substituents on the pyridine ring results in increase in the electron affinity value and, consequently, in the enhancement of the antifungal activity of the compound. The compounds with the electron-donating substituents have greater complexation ability. The main conclusions based on the calculation results are in good agreement with the available experimental data.

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Structural factors have been identified that determine the gas-phase acidity of ortho-substituted benzenesulfonic acid, 2-XC6H4–SO3H, (X = –SO3H, –COOH, –NO2, –SO2F, –C≡N, –NH2, –CH3, –OCH3, –N(CH3)2, –OH). The DFT/B3LYP/cc-pVTZ method was used to perform conformational analysis and study the structural features of the molecular and deprotonated forms of these compounds. It has been shown that many of the conformers may contain anintramolecular hydrogen bond (IHB) between the sulfonic group and the substituent, and the sulfonic group can be an IHB donor or an acceptor. The Gibbs energies of gas-phase deprotonation ΔrG0298 (kJ mol–1) were calculated for all compounds. It has been set that in ortho-substituted benzenesulfonic acids, the formation of various types of IHB is possible, having a significant effect on the ΔrG0298 values of gas-phase deprotonation. If the –SO3H group is the IHB donor, then an ion without an IHB is formed upon deprotonation, and the deprotonation energy increases. If this group is an IHB acceptor, then a significant decrease in ΔrG0298 of gas-phase deprotonation is observed due to an increase in IHB strength and the A− anion additional stabilization. A proton donor ability comparative characteristic of the –SO3H group in the studied ortho-substituted benzenesulfonic acids is given, and the ΔrG0298 energies are compared with the corresponding values of ortho-substituted benzoic acids.