PARAMETRIC METHOD 3 (PM3) STUDY OF THE TAUTOMERIZATION OF 2-PYRIDONE SYSTEMS

The parametric method three (PM3) has been used to predict the optimiz ed geometries of the transition state involved in the tautomerization process of 2-pyridone, its 6-chloro derivative and carbostyril. The es timated activation energies for the hydrogen shift of the three compou nds are 41.2, 41.3 and 44.9 kcal mol-1, respectively. The effect of po lar solvents on the tautomerization process has been discussed by cons ideration of the calculated dipole moments for the reactant, the trans ition state and the product. Examination of OH and NH bond orders reve als a point of inflection in each case in the vicinity of the transiti on state.