Abstract: The basicity strength and stability order of three isomers of diazine in the gas phase were compared by using computational quantum chemistry methods at the B3LYP/6-311+g (d,p) level. The calculation results indicate that the order of basicity strength is pyridazine > pyrimidine > pyrazine. Based on single point energy calculations of optimized structures, the stability order of the isomers is pyrimidine > pyrazine > pyridazine. Similarly, the stability of their conjugated acids follows the same trend: pyrimidine-H > pyrazine-H > pyridazine-H. The distinct thermodynamic properties of pyridazine, such as its combustion heat and standard enthalpy of formation, were qualitatively explained using frontier orbital theory. Incorporating computational chemistry into the teaching of organic acid-base properties and stability helps students deeply understand key concepts, such as Lewis acid-base properties, isodesmic reactions, highest occupied molecular orbitals (HOMO), lowest unoccupied molecular orbitals (LUMO), frontier orbital gaps, and hybrid orbital theory. This approach significantly enhances teaching effectiveness and serves as a valuable tool for improving the quality of organic chemistry education.

Key words: Diazene, Gas-phase basicity, Isodesmic reaction, Computational Chemistry, Hybridization type