The Electronic Structures of Azine Compounds. II. The General Considerations on the Electronic Structures of Azine and Dihydroazine Compounds

Abstract 1) The absorption spectrum of quinoxaline was observed in anhydrous methanol solution. 2) The longest wave-length π-π transition was observed near 31000–33000 cm−1. 3) The MO calculations were made on ten odd aza, azine, and dihydroazine compounds. 4) Comparing the vertical delocalization energies, the most stable isomer was decided as follows. (Remark: Graphics omitted.) 5) Concerning the stabilities of each dihydroazine isomers, the following tendency was observed. The stabilities of dihydroazine isomers increase according to the certain order of molecular symmetry: C2VX→C2h→Vh. 6) The reduction rates of the delocalization energies, azine to dihydroazine compounds, could be a criterion to predict the stabilities of dihydroazine compound as compared with the corresponding azine compounds. When the rate was less than 6%, only the dihydroazine form could exist steadily; more than 17%, the only stable form was the azine form; and between 6-17%, both forms could exist, while the stability of the azine form was surpassed by that of the dihydroazine form near the rate of 9%. 7) The positions of the longest wavelength absorption were predicted or compared with the observed ones. Agreements were satisfactory in the permissible ranges. 8) The molecular diagrams were drawn on several azine and dihydroazine molecules, which could possibly explain the higher stabilities of dihydroazines, the larger skeletons of molecules.