Tautomeric equilibria, H‐bonding and π‐electron delocalization in o‐nitrosophenol. A B3LYP/6–311 + G(2df,2p) study

Tautomeric interconversions (keto–enol and nitroso–oxime combined according to the 1,5‐proton shift into nitrosoenol–ketoxime) and related variations of π‐electron delocalization were studied for o‐nitrosophenol at the B3LYP/6–311 + G(2df,2p) level. The geometry‐ and magnetism‐based indices (HOMA and NICS) were applied to estimate π‐electron delocalization. The relative electronic (ΔE) and Gibbs free energies (ΔG) between the tautomers–rotamers were calculated to estimate tautomeric equilibrium and percentage content of the tautomeric mixture. Aromaticity of the phenyl ring and intramolecular H‐bonding were found to be the main factors stabilizing tautomeric forms (two isomeric nitrosoenols and one ketoxime) via increasing π‐electron delocalization in the chelating (quasi) ring and lowering push–pull interaction between ortho substituents.