Theoretical Investigation of Solvent Effects on Tautomeric Equilibrium of 2-Diazo-4,6-dinitrophenol

The density functional theory has been used to study the tautomeric equilibrium of 2-diazo-4,6-dinitrophenol(DDNP) in the gas phase and in 14 solvents at the B3LYP/6-31G* level. The solvent effects on the tautomeric equilibria were investigated by the self-consistent reaction field theory (SCRF) based on conductor polarized continuum model (CPCM) in apolar and polar solvents and by the hybrid continuum-discrete model in protic solvent, respectively. Solvent effects on the computed molecular properties, such as molecular geometries, dipole moments, E-LUMO, E-HOMO, total energies for DDNP tautomers and transition state, tautomerization energies and solvation energies have been found to be evident. The tautomeric equilibrium of DDNP is solvent-dependent to a certain extent. The tautomer I (cyclic azoxy form) is preferred in the gas phase, while in nonpolar solvents tautomer I and II (quinold form) exist in comparable amounts, and in highly polar solvents, the tautomeric equilibrium is shifted in favor of the more polar tautomer II. (C) 2010 Wiley Periodicals, Inc. Int J Quantum Chem 111: 1115-1126, 2011