Theoretical study of the structure and tautomerism of N1-unsubstituted pyrazoles in the solid state

Abstract

Ab initio theoretical calculations have been performed on the pyrazole cyclic dimer, trimer and tetramers as well as on linear oligomers, assuming that there is no relaxation of the geometry during the proton transfer. The ground state and a wide variety of transition states, corresponding to different pathways for intermolecular proton transfer, have been explored and the results compared with experimental data from crystallography and solid state NMR spectroscopy. For the simplest case of the dimer, the reaction path corresponding to a double proton transfer has been explored as well as the effect of relaxing the geometry.