A theoretical and experimental dipole moment study of annular tautomerism in tetrazole

Abstract

The electric dipole moments of tautomeric 1 H-tetrazole and 2 H-tetrazole have been calculated by the ab initio molecular orbital technique with a 4-31G basis set, and compared with literature experimental values for gaseous C-deuterio-1 H-tetrazole and 2 Htetrazole. Calculated σ and π moments for both tautomers are discussed and compared with previous theoretical values. In 2 H-tetrazole the mesomeric moment outweighs the primary moment corresponding to the classical valence structure, in determining the actual direction of the molecular dipole moment. The calculated total energies are found to be equal for both tautomers. The fact that the dipole moment of tetrazole measured in dioxane (4.88 D) indicates the 1 H form to be the more abundant (78%) is due to a greater Onsager's solvent reaction-field stabilization of the more polar species.