A theoretical study of proton transfers in aqueous para-, ortho-hydroxypyridine and para-, ortho-hydroxyquinoline

The structures and relative stabilities of the four different forms of hydroxypyridine and hydroxyquinoline (normal, protonated cation, deprotonated anion and zwitterion) in the gas phase have been calculated at the Møller-Plesset (MP) perturbation and coupled-cluster theory levels with basis sets up to 6–31+G∗∗. The solvation free energies of the reactions were treated with the SMx series of aqueous solvation models by Cramer and Truhlar. By combining the PM3-SM3 model for solvation with the MP2/6–31+G∗∗ level treatment for the gass-phase species, it is found that the free energy changes of the proton transfer reactions can be predicted reasonably well.