Ab initio modeling of the solvent influence on the azo-hydrazone tautomerism

The solvent effect on the azo (A) -hydrazone (H) tautomeric equilibrium of 1-phenylazo-4-naphthol is modeled by using ab initio quantum-chemical calcu lations. It was found that in methanol, methylene chloride and water there exists a strong hydrogen bonding between the particular tautomer and solven t, as well as dipole-dipole dye-solvent interactions. The results show that the H-form is more stable in water and methylene chloride, while methanol and i-octane stabilize the A-form. The calculational results obtained are i n very good agreement with the experimental data in these solvents publishe d previously. (C) 1998 Elsevier Science Ltd. All rights reserved.