Theoretical Study On The Structures And Properties Of The Isomers Of N₈H₈

The stabilities and properties on energetic material N8H8 have been studied by Gaussisn98 program. The contents which are studied in this thesis are as follows: 1. Theoretical study on the structures and stabilities of the chain isomers of N8H8 2. Theoretical study on the structures and stabilities of the ring isomers of N8H8 3. Theoretical study on the tautomerisms between the chain and ring iso-mers of N8H8 4. Theoretical study on the structures and stabilities of the chain isomers of Nn(CH)8-nH8(n=0~7)Possible isomers and their tautomerisms on energetic material N8H8 and Nn(CH )8-nH8 (n = 0 ~ 7) are optimized by density function theory (DFT). The calculations are performed by B3LYP/6-311++G(d,p) basis set. For each species, the analyses of vibration are performed to obtain the zero point vibrational energies (ZPE) and to verify whether it is a minimum or not. Meanwhile, the electronic charge densities of critical points were calculated with AIM 2000 program package. Furthermore, the orbital interaction is analyzed with the natural bond orbital (NBO) theory. In addition, G3MP2 method is used to obtain more accurate energy and calculate the HOF at 298 K (ΔfHθ(298K)). And we used of Monte-Carlo method with B3LYP optimized structure to estimate the molar volume and density. Nowdays practical conditions limit the experimental researches of hydronitrogen compounds ,so the theoretical studies play a vital part in the field of research, which are mainly focused on ringy conformations. We try to explain the stabilization and tautomerism of isomers on N8H8 and Nn(CH)8-nH8 (n=0~7)through the analysis of conformation, stability, tautomerism, and density.Thirty isomers of chain-N8H8, seventy-four isomers of ring-N8H8, thirty-four isomers of chain- Nn(CH)8-nH8 (n=0~7) and thirty-two isomers of chain- Nn(CH)8-nH8 (n=0~7) have been found in the thesis. The results indicate that the bigger the bond critical point charge densityρis, the shorter the bond length becomes. The results show that the isomers of the chain N8H8 involving N=N were found more stable and their barrier energies of tautomery reactions are higer, so their tautomerisms are also difficult. The research indicate that 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 are the most stable one, while the four-membered-ring are the unstable ones; the energies ,the heats of formation and the density of ring-N8H8 is higher than chain-N8H8; among them the isomerization more difficult, four-member-ring- N8H8 and chain-N8H8 of the lower activation energy conversion, among them more easily isomerization. Simultaneously ,our research results show that the stabilities of the isomers will reduce with the increment of the number of the CH groups to replace nitrogen atoms; the heats of formation of the Nn(CH)8-nH8 molecules decrease along with the replacement of nitrogen atoms by CH groups.