【作者】 张骥；

【导师】 肖鹤鸣；

【作者基本信息】 南京理工大学 ， 材料学， 2003， 博士

【摘要】 多硝基立方烷是非常重要的立方烷衍生物，其具有高张力笼状结构、属于当前热切追求的高能量密度材料（HEDM）。它们在炸药、医药、液晶和高聚物等领域均有广阔的应用前景。为了阐明多硝基立方烷结构、性能及其相互关系，本文运用量子化学中从头计算（ab initio）、密度泛函理论（DFT）和半经验分子轨道（MO）等方法研究了它们的分子几何、电子结构、IR光谱、生成热和其它热力学性质、动力学酸性pK_a、热分解机理以及爆炸和爆轰性质。此外，作为比较和扩充，还计算研究了氰基、异氰基和硝酸酯基立方烷三类化合物的结构和生成热；对于特别重要并具有笼状结构的六硝基六氮杂异伍兹烷（CL-20）的结构和性质也进行了初步研究。概要如下： 1．运用DFT-B3LYP方法，在6.31G^*基组水平下，计算研究了10种多硝基立方烷和CL-20的α（γ）、β、和ε三种构象的分子几何、电子结构、IR光谱和298～1000K温度范围的热力学性质(H°_m、C°_p，m和S°_m)。通过与实验模拟比较，求得B3LYP／6.31G^*水平下适合于多硝基立方烷IR频率精确计算的校正因子为0.9501；据此通过校正计算，报道了多硝基立方烷IR频率的精确理论计算结果。 2．首次通过不破裂立方烷笼状骨架的等键反应设计，并综合运用B3LYP／6-31G^*和半经验MO方法，系统计算了四类立方烷（共21×4=84种）衍生物C₈H_8-m（R）_m（R=-NO₂，-ONO₂，-CN，-NC；1≤m≤8）的精确生成热，探讨了生成热与分子结构的关系。发现多硝基立方烷的生成热具有随取代基数目递变的特殊规律性，从而纠正了先前由基团加和法估算的多硝基立方烷的生成热计算结果。 3．计算结果表明，多硝基立方烷的实验动力学酸性pK_a、分子内用于形成C-H键的环外碳轨道平均s成分（s_a）和分子内的平均C-H伸缩频率（v_a）之间，存在平行的递变关系，这对基于s_a或v_a的数值预估动力学酸性pK_a、进而指导多硝基立方烷和其它相关化合物的合成有助。 4．在非限制性模式下，综合运用DFT、MP2和经选择的MINDO／3半经验MO方法进行计算，阐明了多硝基立方烷的热分解机理。发现热解引发和速控步骤为笼状骨架C-C单键均裂（形成双自由基）；随后，第二个C-C键很快均裂形成产物。在B3LYP／6.31G^*水平下求得八硝基立方烷的热解引发反应活化能为155.30 kJ／mol，表明其具有较高热稳定性和较小感度。一系列计算结果均与实验结果良好地相符。 5.以量子化学计算为基础，求得/又硝基立方烷晶体的升华热、密度和生成热分别为220.63 kJ/mol、2.159 g/cm3和505.54 kJ/mol。由此，按Kamlet--Jaeobs等式估算它的爆速和爆压分别为10.26拓m/s和520.86 kbar，从而表明它作为HEDM的很高研究开发价值。 6.基于B3LYP/6一31G*计算结果，发现在CL一20分子中以N-N键相对较长、其间的电子集居数相对较小，预示N一N键可能较弱;对N一键热解均裂机理进行了计算研究。在CL一20的不同构象中，由前线分子轨道能量及其差值预示的热力学稳定性次序（。a（Y）>p）与实验结果相一致。 总之，本文运用多种量子化学理论方法，对以多硝基立方烷为主的高能笼状化合物的结构和性能进行了系统而广泛的计算研究，所得结果丰富了“立方烷化学”的研究和应用，是该研究领域的最新成果。这对进一步深化这些化合物的理论和实验研究以及对于指导HEDM的寻求都是很有帮助的。更多还原

【Abstract】 Polynitrocubanes are one of the most important derivatives of cubane and belong to the new type of high energetic density materials (HEDM) with high strain and cage structure. They have considerable potential importance in practical applications such as explosives, pharmaceuticals, liquid crystals, and specialty polymers, etc. In order to elucidate the structures and properties of polynitrocubanes, ab initio, density functional theory (DFT) and several semiempirical MO methods are employed to study their molecular geometries, electronic structures, infrared vibrational spectra, heats of formation and the other thermodynamic properties, kinetic acidities pKa, pyrolysis mechanism, and detonation properties. In addition, for comparison, the heats of formation for polycyanocubanes, polyisocyanocubanes, and cubylnitrates are calculated. The structures and properties for hexanitrohexaazaisowurtzitane (CL-20), a very important energetic material with cage structure, are also studied. Brief summary is listed as follows:1. The molecular geometries, electronic structures, IR frequencies, and thermodynamic properties (H m, C P, m and S m) in the temperature range 298 ~ 1000 K are calculated for 10 polynitrocubanes and ( ), p, and s-conformations of CL-20, using the DFT method at the B3LYP/6-31G* level. The accurate IR frequency scaling factor 0.9501 suitable for polynitrocubanes is obtained at the B3LYP/6-31G* level, and the calculated IR frequencies of polynitrocubanes are scaled.2. For the first time the accurate heats of formation for four kinds of derivatives of cubane C8H8-m(R)m (R = -NO2, -ONO2, -CM, and -NC; 1 m 8) and a total of 84 compounds (21 4) are systematically calculated, using both DFT-B3LYP/6-31G* method via designed isodesmic reactions in which the cubane cage skeleton has been kept and semiempirical MO methods. The relationships between the heats of formation and molecular structures are discussed. It is found that with increasing in the number of nitro groups, the trend of changes for the heats of formation of polynitrocubanes is.exceptional. Therefore, the previous data of heats of formation of polynitrocubanes estimated from groupadditivity method are corrected.3. Calculations indicate that, for polynitrocubanes, there are parallel relationships between their experimental kinetic acidities pKa, the average s characters (sa) in the exocyclic carbon orbital used for the C-H bonds within each molecule, and the average C-H stretching frequencies (va) within each molecule. These calculated results are helpful to the estimations of the kinetic acidities pKa of polynitrocubanes and the other type of compounds based on the values of sa or va , which has reference value for organic syntheses.4. The pyrolysis mechanism of polynitrocubanes is elucidated using various theoretical methods, i.e. MP2, DFT and selected MINDO/3 semiempirical MO, based on the unrestricted model. The calculated results show that the pyrolysis initiation reaction of polynitrocubanes, i.e. rate-controlling step, is to form a diradical by the single C-C bond breaking in the cube. The second C-C bond breaking is easily followed. The calculated activation energy for the pyrolysis initiation reaction of octanitrocubane, obtained from B3LYP/6-31G* method, is 155.30 kJ/mol, indicating that octanitrocubane has better thermal stability and less sensitivity. A series of calculated results are in good agreement with the experimental results.5. Based on the calculations from quantum chemistry, the sublimation enthalpy, density and heat of formation for octanitrocubane crystal are 220.63 kJ/mol, 2.189 g/cm3 and 505.84 kJ/mol, respectively. According to Kamlet-Jacobs equations, the estimated detonation velocity and detonation pressure of octanitrocubane are 10.26 km/s and 520.86 kbar, respectively, indicating that octanitrocubane has highly exploitable values as HEDM.6. Based on the B3LYP/6-31G* calculations, it is found that, in CL-20, t更多还原