Heteroaromaticity .10. The direct calculation of resonance energies of azines and azoles from molecular dimensions

A simple method is presented for the direct calculation of thermodynamic resonance energies of aza heterocycles from their molecular dimensions. This method, which is derived from the HOSE approach of Krygowski, provides values for a range of azines and fused azoles which are in satisfactory agreement with those obtained by other methods. In the case of 1,2-diazines an energy of repulsion of ca 9.5 Kcal, mole(-1) between the nitrogen lone pairs has been estimated and some consequences of this observation for the stability of polyazines are discussed. (C) 1997 Elsevier Science Ltd.