N8H8环状异构体的结构与稳定性的理论研究

采用密度泛函理论的B3LYP方法在6-311 G**基组水平上对N8H8氮氢环状化合物可能存在的构型进行了几何优化,得到74种稳定异构体,应朋A然键轨道理论NBO和分子中的原子理论AIM分析了这些化合物成键特征和相对稳定性,G3MP2方法汁算了各异构体的能量及生成热.研究结果表明:N原子孤对电子到相邻的氮氮键的超共轭作用是影响氮氮键长变化的丰要因素;N8H8环状异构体的稳定性顺序为:六元环>七元环>八元环,五元环>三元环>四元环,六元环是这些N8H8环状异构体中最稳定的,最不稳定的是四元环,G19是所有环状异构体中能量最低的:M3能量最高,稳定性最差,A7密度最大.     

N8H8链状异构体结构与稳定性的理论研究

采用密度泛函理论(DFT), 在B3LYP/6-311＋＋G(d,p)基组上计算得到了21种N₈H₈链状异构体, 并研究了这些异构体间可能的互变异构情况. 为了得到更为精确的能量信息, 计算了QCISD(T)/6-311G(d,p)基组水平上各物质的能量. 所得的21种异构体分为4类(4种类型链状化合物): A为直链, B有一个支链, C有2个支链, D有3个支链; D类只有一种, A类稳定构型2种, B类稳定构型12种, C类稳定构型6种; 相对稳定的分别为: B2-1构型, B2-3构型和C23-2构型. 我们研究发现N₈H₈链状异构体中含有明显N＝N双键特征有利于化合物稳定性的提高.     

N6H6结构和性质的理论研究

采用密度泛函理论的b3lyp方法在6-311＋＋G**基组上对15种分子式为N₆H₆的氮氢化合物进行了理论计算, 并且应用了自然键轨道理论(Nature Bond Orbital, NBO)和分子中的原子理论(Atoms In Molecules, AIM)分析了这些化合物的成键特征和相对稳定性. NBO分析表明N原子孤对电子到相邻的氮氮键的超共轭作用是影响氮氮键长变化的主要因素, AIM计算的氮氮键的键临界点电荷密度与键长呈反比关系. 而且, NBO的立体和超共轭分析表明立体交换排斥能和超共轭作用对这些分子的相对稳定性起了重要作用. G3MP2计算结果表明氮氢化合物的生成热均为正, 并且环状分子的能量和生成热都高于链状分子.     

N6H6结构和性质的理论研究

采用密度泛函理论的b3lyp方法在6-311＋＋G**基组上对15种分子式为N₆H₆的氮氢化合物进行了理论计算, 并且应用了自然键轨道理论(Nature Bond Orbital, NBO)和分子中的原子理论(Atoms In Molecules, AIM)分析了这些化合物的成键特征和相对稳定性. NBO分析表明N原子孤对电子到相邻的氮氮键的超共轭作用是影响氮氮键长变化的主要因素, AIM计算的氮氮键的键临界点电荷密度与键长呈反比关系. 而且, NBO的立体和超共轭分析表明立体交换排斥能和超共轭作用对这些分子的相对稳定性起了重要作用. G3MP2计算结果表明氮氢化合物的生成热均为正, 并且环状分子的能量和生成热都高于链状分子.     

N5H5异构体的结构与稳定性的理论研究

采用密度泛函理论的B3LYP方法在6-311++G**基组水平上对N5H5氮氢化合物异构体可能存在的构型进行了几何优化, 得到23种稳定异构体, 并研究了这些异构体间可能的互变异构情况. 为了讨论N5H5异构体作为含能材料候选物质的可能性, 还采用了G3B3方法计算了能量, 并且计算了异构体的生成热(⊿Hf,298).结果表明, 在23种异构体中链状异构体最稳定, 四元环四氮烷异构体最不稳定, 存在一个N=N双键的异构体较同类异构体能量低, 较为稳定; N5H5氮氢化合物的生成热均为正, 其中异构体E1生成热最高. 估算了N5H5的摩尔体积, 由密度公式ρ=MT/Vmol,得到E1 的密度最大.     

叠氮化合物C6H6-n(N3)n(n=1~6)的密度泛函理论研究

运用密度泛函理论, 在B3LYP/6-31G*水平上, 对叠氮化合物C6H6-n(N3)n(n=1~6)进行理论计算, 并对所得到的几何结构进行了振动频率分析. 计算结果表明, 这些化合物是热力学稳定的. 基于自然键轨道理论, 分析了稳定结构的电荷分布及成键情况. 在不破坏苯环和叠氮基的原则下, 设计等键反应计算了这些化合物的生成热, 结果表明, 标题化合物的生成热都很高, 且随着叠氮基数目的增加而线性增大.     

羰基硼化合物B2n(CO)n (n＝1～6)的理论研究

运用密度泛函理论(DFT)的B3LYP/6-31G*方法, 对羰基硼化合物B_2n(CO)_n (n＝1～6)各种可能的结构进行了优化,对它们的几何构型、电子态、振动频率、核独立化学位移(NICS)和B₂CO的分子轨道进行了理论研究, 得到了B_2n(CO)_n (n＝1～6)结构的稳定性信息. 在它们的基态结构中, 羰基的配位方式是端配位(μ₁-CO), B_2n(CO)_n (n＝1～5)的基态构型是线形或平面结构, B₁₂(CO)₆的基态构型则较为复杂. B_2n(CO)_n (n＝1～3)的基态是三重态, B_2n(CO)_n (n＝4～6)的基态是单重态. 振动频率和轨道的研究为实验提供了重要的理论依据.     

气体再燃低NOx燃烧中NO与NHi的反应机理研究

采用量子化学密度泛函理论(DFT)对NO与NH_i自由基的反应机理进行了研究,并结合经典过渡态理论对各反应速率常数进行了计算。结果表明,NO与NH₂自由基的反应体系可通过六个反应通道形成N₂+H₂O、N₂O+H₂和N₂H+OH。从能量变化和反应速率两方面考虑,产物N₂+H₂O最容易生成,其最佳反应通道为NO+NH₂→→N₂+H₂O;NO与NH自由基的反应体系可通过七个反应通道形成N₂+OH、N₂O+H和N₂H+O;其中,N₂+OH最容易生成,最佳反应通道为NO+NH→→N₂+OH。比较发现, NH比NH₂自由基更易与NO发生反应生成N₂。因此,在实际运行中改变操作条件,实现NH₂等向NH方向转化,有利于NO_x的还原。     

羰基硼化合物B2n(CO)n (n＝1～6)的理论研究

运用密度泛函理论(DFT)的B3LYP/6-31G*方法, 对羰基硼化合物B_2n(CO)_n (n＝1～6)各种可能的结构进行了优化,对它们的几何构型、电子态、振动频率、核独立化学位移(NICS)和B₂CO的分子轨道进行了理论研究, 得到了B_2n(CO)_n (n＝1～6)结构的稳定性信息. 在它们的基态结构中, 羰基的配位方式是端配位(μ₁-CO), B_2n(CO)_n (n＝1～5)的基态构型是线形或平面结构, B₁₂(CO)₆的基态构型则较为复杂. B_2n(CO)_n (n＝1～3)的基态是三重态, B_2n(CO)_n (n＝4～6)的基态是单重态. 振动频率和轨道的研究为实验提供了重要的理论依据.     

用密度泛函理论研究一种新型有机硅化合物异构体的振动光谱

在B3LYP/6-31＋G(d)的水平上, 对两种含有手性Si原子的新型有机硅单体Si₂(CH₃)₂H₂N₂(C₂H₅)₄和Si₄(CH₃)₄H₄N₂(C₆H₅)₂的几种异构体进行了研究, 在全参量几何构型优化的基础上, 进行了简谐振动频率计算, 同时对所研究的体系进行了热力学性质和低能激发态的含时密度泛函理论(TDDFT)计算. 理论计算表明, 构象异构体之间的红外光谱差异不大, 热力学和低能激发态性质也相似; 顺/反结构相似的异构体之间红外光谱差异不大, 但热力学和低能激发态性质却呈现差异; 旋光异构体或顺/反结构相差较大的异构体之间, 红外光谱和热力学及低能激发态性质有明显的差异. 从理论上解释了实验红外光谱中Si—H振动峰的裂分是由异构体的存在所致, 并找到裂分峰所对应的异构结构. Si—H键振动频率与其键长相关.     

Theoretical study on the structures and stabilities of the isomers of N6H6

Forty-eight possible isomers of N₆H₆ have been investigated at the B3LYP/6-311++G^** and G3B3 levels. The results show that heats of formation of all isomers are positive and A2-3 is the lowest and C2 is the highest. In addition, the energies and the heats of formation of the ring-shaped isomers are higher than those of the chain-shaped isomers. Among the ring-shaped isomers, the four-membered ring isomers have the highest heat of formation and the five-membered ring isomers have the lowest. For six-membered ring isomers, only the chair-shaped isomers are stable. Among all those chain-shaped isomers, the ones which have N–N bond and its length is in the range of NN double bond can improve the stability of the compounds.     

Theoretical predictive study on N7H7 hydronitrogen compounds

Geometric structures and energy properties of 25 isomers of N₇H₇ hydronitrogen compounds have been studied at the B3LYP/6-311++G(d,p) level. Atoms in molecules (AIM) and nature bond orbital (NBO) theories are applied to analyze the bond nature and the origin of structure and energy variations. The result indicates that the hyperconjugation from the lone pair of nitrogen to the neighboring NN bond plays an important role in the NN bond length variation and the relative stability of the 25 isomers can be attributed to the steric and hyperconjugative effects. G3MP2 calculations show that the heats of formation (HOFs) of all the isomers, especially those of the cyclic isomers, are positive and large, suggesting their potential to be energy molecules. Furthermore, the HOFs of the cyclic isomers decrease with increase of the number of substituents.     

卤代二硫烷互变异构体相对稳定性的理论研究

由于在有机合成化学、生命科学、大气化学和环境保护中的重要性,含有S=S键的过硫化物(硫烷)XSSX(X=H,CH3,F,Cl等)得到广泛研究。过硫化物XSSX可以有如图1所示的2种异构体,一种是与过氧化氢结构类似的非平面型的线型结构(属于C2点群),另一种是硫代亚砜型的分叉型构型(SSX2,属于C     

Theoretical study on the structures and properties of the isomers of Nn(CH)8−nH8 (n = 0–7)

With replacement of N atoms by CH groups in the most stable chain isomer of N8H8, 34 possible isomers of N_n(CH)_8−nH₈ (n = 0–7) have been designed and optimized at the B3LYP/6-311++G** level of theory. The natural bond orbital (NBO) and atoms in molecules (AIM) analysis are carried out to study the bonding nature and relative stabilities of these conformers. G3MP2 method is applied to calculate energies and heats of formation. The results indicate that the hyperconjugation effect from lone pairs of nitrogen atoms to germinal C–N bonds is the major factor which caused the change of the C–N bond length. With the more replacement of nitrogen atoms by CH groups, the heats of formation of the isomers of N_n(CH)_8−nH₈ (n = 0–7) decrease gradually, but the energies increase linearly.     

Theoretical prediction on heats of formation for polyisocyanocubanes

The heats of formation (HOF) for all the 21 polyisocyanocubanes are calculated systematically with density functional theory (DFT) B3LYP and semiempirical MO(MINDO/3, MNDO, AM1 and PM3) methods. First, the accurate HOFs for the 8 title compounds are obtained by means of designed isodesmic reactions at DFT-B3LYP/6-31G* level, and the cubane cage skeleton has not been broken (i.e. choosing cubane as a reference compound) to produce more accurate and reliable results. It is found that there are good linear relationships between the HOFs calculated using the B3LYP/6-31G* and four semiempirical MO methods, respectively, and all of the linear correlation coefficients are more than 0.9971. The HOFs obtained from PM3 calculation are the best among the four semiempirical MO methods. Then, the accurate HOFs at B3LYP/6-31G* level of other 13 polyisocyanocubanes are obtained by systematically correcting their PM3-calculated HOFs. Polyisocyanocubanes have very high HOFs, and the HOFs increase linearly with the increasing of the number of isocyano groups in a molecule. The results show that polyisocyanocubanes are the new generation explosives with highly potential and exploitable value.     

Theoretical study on the ring-opening isomerization reaction mechanism of the ring isomers of N8H8

Ring-opening isomerization from ring-shaped isomers to chain-shaped isomers of N(8)H(8) has been studied by a density function B3LYP method at 6-311+ +G** level. 20 ring-shaped isomers have been found to be able to transform into chain-shaped isomers, with 20 possible transition states got by ring-opening structure optimization. Furthermore, the ring-openings have been found in the longer N-N single bond by analyzing the length change of N-N bond of ring-shaped isomers in ring-opening processes. In addition, with the activation energies in ring-opening processes, the differences of the activation energies in isomerization between the isomers have been found according to the classification of rings. The activation energies in ring-opening isomerization of six-membered ring-shaped isomers are higher than that of the four-membered ring-shaped isomers. It indicates that six-membered ring-shaped isomers difficult in ring-opening in the isomerization are the steadiest ring-shaped isomers of N(8)H(8) while four-membered ring-shaped isomers easy in ring-opening are the most unstable.