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Experimental And Theoretical Study Of The Molecular Reactions Of Nitro Compounds

Posted on:2013-06-22Degree:DoctorType:Dissertation
Country:ChinaCandidate:C Y ZhangFull Text:PDF
GTID:1221330434471171Subject:Physical chemistry
Abstract/Summary:PDF Full Text Request
Safety and power density are the two most concerned properties of explosives. The explosives safety is governed by its decomposition characteristics under certain stimulation conditions. Most of the applied explosives are nitro compounds, it is practically and theoretically important to study the molecular decomposition mechanism of nitro compounds in understanding, assessment and control of explosives security. The experimental study is usually challenging as the explosive reactions are fast, complex and means of variable features. In this work, some important reactions initiating the molecular decomposition of nitro compounds of explosives including NO2partition, NO2/ONO isomerization and hydrogen transfer were investigated using matrix isolation infrared spectroscopy and quantum chemical and molecular forcefield calculations.The nitro-nitrite isomerization reactions of the most simple nitro compounds including CH3NO2, CH2(NO2)2, CH(NO2)3and C(NO2)4were theoretically studied using the (U)B3LYP/6-311++G(3df,2p) and (U)CCSD(T)/cc-pVTZ methods. The results showed that among the isomers of the nitro compounds except CH3NO2, the molecular stability increases with the number of nitrite (ONO) groups. It was found that there is a synergistic effect of the bond strength variation in the CONO fragment. That is, the weakening of the CO-NO bond is accompanied by the strengthening of the C-ONO and CON-O bonds, and vice versa. The isomerization and dissociation reactions of dinitrobenzene (DNB) were also studied using the (U)B3LYP/6-311++G(d,p) method. The results showed that the most readily reaction takes place along the NO2/ONO isomerization followed by O-NO dissociation to give NO. Some interesting structures with high symmetry and stability were found to be the potential intermediates in the DNB decomposition processes. In addition, a combined quantum-chemistry and molecular forcefield method was employed to investigate the different effects of pH in aqueous solution on the explosive HMX degradation. It was found that an alkaline aqueous solution can significantly promote the HMX degradation, whereas the acidic aqueous solution cannot, in good agreement with the experimental observations.In addition to theoretical studies, matrix isolation infrared absorption spectroscopy is employed to study the photochemistry of explosive models nitotoluene (NT), nitroaniline (NA) and nitrophenol (NP), and an applied explosive 1,3,5-trinitrotoluene (TNT). The hydrogen-transferred products (HTP) of ortho-NA and TNT, and the nitrite isomers of NT, meta-/para-NA and meta-/para-NP were trapped and identified. Their infrared absorptions were assigned with the aid of B3LYP/6-311++G (d,p) frequency calculations. It was found that the hydrogen atom transfer isomerization product is re-converted to the reactant o-nitrotoluene on annealing, consistent with theoretical predictions that there is a very low energy barrier for the rearrangement reaction of the hydrogen atom transfer product to ortho-NT. All the nitrite compounds are unstable which can be easily decomposed to NO, implying that the previously observed NO elimination reaction is experienced the NO2/ONO isomerization. These findings suggest that low-temperature matrix isolation infrared spectroscopy is an effective method to trap and detect the active intermediates of explosive decomposition reactions, which play a critical role in understanding the decomposition mechanism of explosives.
Keywords/Search Tags:nitro compound, NO2partition reaction, hydrogen-transfer reaction, NO2/ONO isomerization, matrix isolation infrared spectroscopy, and quantumchemistry
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