Theoretical calculations on the tautomerization of five tetrazole derivatives are performed with MNDO MO method. The results show that the migrating groups (R^2) in the transition states lie above the tetrazole ring planes. The geometries of transition states are determined mainly by R^2 whereas the substituent (R^1) on C(5) hardly affects the geometries. The electron-withdrawing character of R^2 has a great effect on the activation energy while R^1 has fewer effects on it. There are good linear relationships between the activation energies and bond orders of the breaking bonds and the activation energies and charges on R^2 groups in the reactants respectively. The equilibrium constant is affected by the characters of substituents (R^1 and R^2). The greater the electron-withdrawing character of R^1, the larger the equilibrium constant. On the contrary, increasing of the electron-withdrawing character of R^2 makes the equilibrium constant smaller.

Key words: TETRAZOLE P, TAUTOMERISM, ACTIVATION ENERGY, EQUILIBRIUM CONSTANT