Seventy-four possible steady isomers of ring-N₈H₈ have been optimized by a density function B3LYP method at 6-311＋＋G** level NBO (nature bond orbital) and AIM (atoms in molecules) were used to discuss bond nature and relative stabilities of these conformers. Energies and heats of formation were calculated by a G3MP2 method. The result indicates that the hyperconjugation effect from lone pairs of the nitrogen atoms on its neighboring N—N bonds is the main factor that affects the length of N—N bond. The relative stability order of the isomers of ring-N₈H₈ is as follows: six-membered-ring＞seven-membered-ring＞eight-membered-ring; five-membered-ring＞three-membered-ring＞four-membered-ring. Among all the conformers, six-membered-ring isomers are the most stable ones while the four-member-ring isomers are the most unstable ones. In addition, G19 has the lowest energy. M3 has the highest energy, so it is the most unstable isomer. The density of A7 is the largest.

Key words: hydronitrogen compound, density functional theory (DFT), energy, heat of formation