Hartree-Fock and density functional theory studies on tautomerism of 5,5′-diisopropyl-3,3′-bipyrazole in gas phase and solution

To gain a better understanding of the tautomerism of 5,5'-diisopropyl-3,3'-bipyrazole, theoretical studies were performed using the ab initio HF and DFT methods. Several structural and molecular properties, total molecular energies, relative energetic stabilities, tautomeric equilibrium constants, kinetic parameters, Mulliken net charges and pK(a) values for three tautomers were calculated. Tautomer I presenting a large junction distance between the pyrazolic rings is the most stable. Forms II and III have respectively higher dipole moment and more acidic character. (C) 2013 Elsevier B.V. All rights reserved.