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 pi-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 pi-electron delocalization. The relative electronic (Delta E) and Gibbs free energies (Delta G) 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 pi-electron delocalization in the chelating (quasi) ring and lowering push-pull interaction between ortho substituents. Copyright (c) 2005 John Wiley & Sons, Ltd.