Structure and Reactivity of Uracil Derivatives. Thermodynamic Stability of 5-Diazouracil

The equilibrium position in the electrocyclization of certain model diazo compounds has been calculated using ab initio calculations based on RHF/6-31G with full optimization of the geometry. It was shown that on reducing the NN bond length the position of equilibrium is displaced towards the acyclic isomer. This effect is expressed to the greatest extent in -diazocarbonyl systems to which 5-diazouracil derivatives belong. An unusual polarized electron distribution was apparent for 5-diazouracil itself, which does not correspond with the classical Lewis structure.