This paper is a density functional theory (DFT) calculation of intramolecular proton transfer (IPT) in 6-hydroxypicolinic acid (6HPA, 6-hydroxypyridine-2-carboxylic acid) tautomeric forms. The transition state for the enol -to- keto transition is reported in the gas phase and in four different solvents. The planar dimer of 6HPA keto forms and nonplanar dimer of 6HPA enol forms in the gas phase theoretically was studied too. The IPT reactions and dimerization processes were studied at the B3LYP/6-31++G(d) basis set level of the theory. The influence of the solvent on the tautomerization reaction of 6HPA was examined using the conductor-polarizable continuum model (CPCM). The IPT reaction in the gas phase is almost the same as solution. The dimerizations energies were also estimated as the results showed that the stability of 6HPA tautomer dimer structures is directly affected by the distance of intermolecular hydrogen bonding and electrostatic potential (ESP) value in the tautomer dimer.

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