Computational study of the intramolecular proton transfer reactions of dipicolinic acid (pyridine-2,6-dicarboxylic acid) and its dimers

► N is found by calculations to be more stable than Z. ► IPT between Z and N is very easier in the gas phase. ► The NN is more stable than ZZ by 0.95 kcal/mol. ► Two hydrogen bonds in NN and ZZ are equivalent to each other.