Theoretical investigation of tautomeric equilibrium in ortho-hydroxy phenyl Schiff bases

The main objective of this Letter is to show the relationship between aromatic and chelate formations during changes in tautomeric equilibrium. The impact of both the environment's polarity (modelled by SCRF method) and substitutions on tautomeric equilibrium in ortho-hydroxy aryl Schiff bases was elaborated by MP2/6-311+G(d,p) calculations. The aromaticity of the phenyl and chelate fragments versus tautomeric equilibrium was studied using the aromaticity indices and structural data calculated by the ab initio method. The obtained results undoubtedly show that the aromaticity indices can be a criterion in defining the particular prevailing tautomeric form.