取代氯苯化合物的电子结构和键离解能的理论研究

利用密度泛函（DFT）三种交换／相关函数（B3LYP,B3PW91,B3P86）结合6—31G^＊＊和 6-311G^＊＊基组,计算了13个取代氯苯化合物的键离解能．结果表明B3PS6／6—311G^＊＊方法是计算取代氯苯化合物键离解能的可信方法,研究发现C—Cl键的键离解能与所使用的基组和计算方法密切相关,取代基对C—Cl键的键离解能的影响不明显．研究了目标化合物的前线轨道能级差,并对取代氯苯化合物的热稳定性做了评估．     

薁X-H(X=CH2, NH, O)键离解能取代基效应的理论研究

本文利用UB3LYP/6-311++g(2df,2p)//UB3LYP/6-31+g(d)方法，首次就对位取代薁系列化合物(Y-C10H8X-H)的X-H(X=CH2, NH, O)键离解能进行了理论研究。结果发现，除了6-取代-2-甲基薁，取代基对薁X-H键离解能的效应与苯大致相同。然而，由于薁结构中固有偶极矩与不同取代基的电子效应相互作用，对位取代的羟基薁和氨基薁的反应常数( )变化非常显著。利用GE/RE和SIE理论方法，研究发现虽然基态效应在决定净取代基效应的大小中起了一定作用，但取代基效应主要来源于自由基效应的影响。     

取代基对木质素三聚体模型化合物醚键均裂反应影响的密度泛函理论研究

利用密度泛函理论M062X/6-31++G(d,p)方法,对27种具有不同取代基(甲基、羟甲基和甲氧基)的木质素三聚体模型化合物的Cα-O和Cβ-O键均裂解离能进行了理论计算,探究了不同位置取代基对醚键解离能的影响规律。结果表明,当R2或R3位氢原子仅有一个被甲氧基取代时,Cβ-O键解离能变化很小;当R2、R3位氢原子均被甲氧基取代时,Cβ-O键解离能明显降低;且R4、R5位甲氧基能强化R2、R3位甲氧基对Cβ-O键解离能的降低程度,而不受R1位取代基的影响。当R4、R5位氢原子相继被甲氧基取代时,Cα-O键解离能逐渐降低,且R2、R3位甲氧基也能强化R4、R5位甲氧基对Cα-O键解离能的降低程度。当R1位氢原子相继被甲基、羟甲基取代时,Cα-O键解离能逐渐升高,然而R2、R3位甲氧基会弱化R1位甲基、羟甲基对Cα-O键解离能的升高程度;R1位甲基不会影响Cβ-O键解离能,羟甲基却能明显提高Cβ-O键解离能。     

聚对苯二甲酸乙二醇酯二聚体模化物键离能的理论研究

采用密度泛函理论方法计算了聚对苯二甲酸乙二醇酯(PET)二聚体模化物的键离能,并设计PET热解的3条可能路径,分析PET热解机理.由于乙酸甲酯与PET具有相同的酯基官能团,因此以乙酸甲酯为简单模型参照物,采用M06-2X,B3P86,B3LYP以及BHandHLYP方法分别在基组LanL2DZ,6-31G(d),3-2...     

卤代甲烷的键离解能与取代基效应

将芳环上取代基的电子效应参数引入卤代甲烷, 以卤代甲烷分子Y-CH_nX_{3－n (n＝0～3; Y＝H, F, Cl, Br, I; X＝F, Cl, Br, I)中Y-C键的标准键焓 与中心C原子相键连原子的场/诱导效应之和ΣFi、共轭效应之和ΣRi以及诱导偶极之和Σ(α×F)为参数, 建立了一个定量估算卤代甲烷分子中Y-C键离解能(BDE)的通用模型, BDE(Y-C)＝57.5460＋0.8855 －101.0780ΣRi－64.8390ΣFi－10.1034Σ(α×F). 对35个C-H, C-F, C-Cl, C-Br和C-I键回归分析结果表明, 估算Y-C键离解能的精度在实验误差范围内. 对外部数据集的预测结果表明, 该模型具有较高的预测精度, 可用于预测还没被实验测定的卤甲烷中Y-C键离解能. 还对卤代甲烷中104个C-Y键的键离解能进行了预测. 将芳环上取代基效应用于研究饱和体系化学键性能, 有利于深入理解取代基效应对化学键性能的影响.}     

含氮药物分子中氮a-位碳氢键离解能的理论研究

本文利用G3B3 和CBS-Q高精度理论方法检验了一系列胺类有机化合物中α-碳氢键离解能的实验测量值,在此基础上筛选出(U)BHandH/6-311++G(2df, 2p)//(U)B3LYP/6-31G(d)方法,发现其可以准确快速的预测氮α-碳氢键离解能。运用该方法研究了若干含氮药物分子,发现氮α-碳氢键离解能随药物分子结构发生明显变化。为了阐明其变化规律,系统研究单取代和双取代基效应,并解释了不同取代基效应的来源。     

环境污染物中碳氯键离解能的理论研究

利用六种密度泛函理论方法（B3LYP, B3P86, MPW1K, TPSS1KCIS, X3LYP, BMK）对碳氯键离解能进行理论计算,结果发现几种新发展的密度泛函(DFT)方法用于碳氯键离解能的计算比传统的B3LYP有较大的改善,其中对能量估算相对准确的B3P86方法对碳氯键离解能的计算精度最高,对17个分子中碳氯键离解能计算的平均绝对偏差为6.58 kJ/mol。最后运用B3P86方法对一系列环境危害较大,但可通过光化学降解和生物降解的氯代有机物的碳氯键离解能值进行预测,并讨论了影响碳氯键离解能的结构性质关系。     

木质素模化物紫丁香酚热解机理的量子化学研究

采用密度泛函理论方法B3LYP/6-31G++(d,p),对木质素模化物紫丁香酚的热解反应机理进行了量子化学理论研究。提出了三种可能的热解反应途径,对各种反应的反应物、产物、中间体和过渡态的结构进行了能量梯度全优化。计算了各热解反应途径的标准动力学参数,分析了各种主要热解产物的形成演化机理。键离解能计算结果表明,紫丁香酚中CH₃-O键的键离解能最小,各种键离解能的大小顺序为CH₃-O < O-H < CH₃O-C_aromatic < CH₂-H < HO-C_aromatic < C_aromatic-H。在反应路径(1)中,主要热解产物是3-甲氧基邻苯二酚,其形成反应的总能垒为366.6 kJ/mol;在反应路径(2)中主要热解产物是2-甲氧基-6-甲基苯酚,其形成反应的总能垒为474.8 kJ/mol;在反应路径(3)中形成邻甲氧基苯酚的总能垒很低,为21.4 kJ/mol,这表明,在连接甲氧基的碳原子上加氢后能够有效地降低木质素芳环模化物紫丁香酚去甲氧基反应的反应能垒。     

取代基效应对褐煤模型化合物离解焓影响的理论研究

为了探究褐煤热解过程中氧桥键C-O均裂这一重要反应, 选取α-O-4和β-O-4类结构单元作为褐煤模型化合物, 运用不同密度泛函计算了部分模型化合物中C-O的离解焓, 并以CBS-QB3作为理论基准值进行比较, 最后选取M05-2X进行离解焓计算. 结果显示, 对于选定的α-O-4和β-O-4类模型化合物, 其平均离解焓分别为51.0 kcal/mol和66.1 kcal/mol. 周围取代环境能显著影响C-O离解焓, 芳环上存在给电子基团(OH, OCH₃和CH₃)能降低C-O离解焓, 而吸电子基团COOH则能增加其离解焓. 然后深层次分析了取代基效应对C-O离解焓的影响. 此外, 分子内氢键的形成对离解焓也有很大的影响. C-O的离解焓与其键长没有特定的相关性, 不能简单的通过C-O键长来预测其离解焓.     

DFT study of the C-Cl bond dissociation enthalpies and electronic structure of substituted chlorobenzene compounds

Quantum chemical calculations were used to estimate the bond dissociation energies (BDEs) for 13 substituted chlorobenzene compounds. These compounds were studied by employing the hybrid density functional theory methods (B3LYP, B3PW1, B3P86) with 6-31G** and 6-311G** basis sets. It was demonstrated that B3P86/6-311G** method is the best method for computing the reliable BDEs for substituted chlorobenzene compounds which contain the C-Cl bond. It was found that the C-Cl BDE depends strongly on a computational method and basis set used. Substitution effect on the C-Cl BDE of substituted chlorobenzene compounds is further discussed. It is shown that the effects of substitution on the C-Cl BDE of substituted chlorobenzene compounds are very insignificant. Frontier orbital energy gap of studied compounds was also investigated. From the data on frontier orbital energies gap, we estimated the relative thermal stability of substituted chlorobenzene compounds.     

The C−NO2 bond dissociation energies of some nitroaromatic compounds: DFT study

The C−NO₂ bond dissociation energies in nitrobenzene; 3-amino-nitrobenze; 4-amino-nitrobenze; 1,3-dinitrobenzene; 1,4-dinitrobenzene; 2-methyl-nitrobenzene; 4-methyl-nitrobenzene; and 1,3,5-trinitrobenzene nitroaromatic molecules, are computed using B3LYP, B3PW91, B3P86 three-parameter hybrid Density Functional Theory (DFT) methods in conjunction with 6-31G^** basis set. By comparing the computed energies and experimental ones, it is found that B3P86/6-31G^** is not capable of predicting the satisfactory bond dissociation energy (BDE). The BDEs computed with both B3LYP/6-31G^** and B3PW91/6-31G^** for the nitroaromatic molecules are closer to the experimental ones than those obtained with B3P86/6-31G^**. But, when compared with the experimental one, the BDE from the B3LYP/6-31G^** has the maximum deviation, which is completely outside our desired target accuracy for chemical predictions (less than 2.00 kcal mol⁻¹). Therefore, we suggest B3PW91/6-31G^** method as a reliable method of computing the BDE for removal of the nitrogen dioxide group in the nitroaromatic compounds. In addition, the C−NO₂ BDEs for 2,4,6-trinitrotoluene (TNT), triaminotrinitrobenzene (TATB), diaminotrinitrobenzene (DATB), and picramide are studied with B3PW91/6-31G^** method.     

Theoretical calculation of bond dissociation energies and heats of formation for nitromethane and polynitromethanes with density functional theory

The C? NO₂ bond dissociation energies (BDEs) and the heats of formation (HOFs) of nitromethane and polynitromethanes (dinitromethane, trinitromethane, and tetranitromethane) system in gas phase at 298.15 K were calculated theoretically. Density functional theory (DFT) B3LYP, B3P86, B3PW91, and PBE0 methods in combination with different basis sets were employed. It was found that the C? NO₂ bond BDEs can be improved from B3LYP to B3PW91 to B3P86 or PBE0 functional. Levels of theory employing B3P86 and PBE0 functionals were found to be sufficiently reliable without the presence of diffusion functions. As the number of NO₂ groups on the same C atom increases, the PBE0 functional performs better than the B3P86 functional. Regarding the calculated HOFs, all four functionals can yield satisfactory results with deviations of <2 kcal mol^?1 from experimental ones for CH₂(NO₂)₂ and CH(NO₂)₃, when the diffusion functions are not augmented. For the C(NO₂)₄ molecule, the large basis sets augmented with polarization functions and diffusion functions are required to yield a good result. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Theoretical studies of bond dissociation energies for removal of the nitrile group in some nitrile compounds

The CCN bond distances and bond dissociation energies (BDEs) are estimated by utilizing quantum chemical calculations for 16 nitrile compounds. Since DFT methods have been researched to have low basis sets sensitivity for small and medium molecules in our earlier work [Jun Zhao, Xinlu Cheng, Xiangdong. Yang, J. Mol. Struct. (Theochem) 766 (2006) 87] 16 nitrile compounds are studied by employing the hybrid density functional theory (B3LYP, B3PW91, B3P86) and the complete basis set (CBS-Q) method in conjunction with the 6-311G^** basis set. The obtained results are compared with the available experimental data. It is demonstrated that CBS-Q method, which can produce reasonable BDEs for some systems, seems unable to predict accurate BDEs here. While, the B3P86 calculated results agree very well with the experimental values. So B3P86 method is suitable for computing the reliable BDEs of CCN bond for nitrile compounds.     

Quantum Monte Carlo calculations of bond dissociation energies for some nitro and amino molecules

Bond dissociation energies (BDEs) for some nitro or amino contained prototypical molecules in energetic materials are computed by fixed‐node diffusion quantum Monte Carlo method. The nodes are determined from a Slater determinant calculated within density functional theory at the B3LYP/6‐311G** level. The possible errors, the nodal error, and the cancellation of nodal errors in calculating BDE are discussed, and the accuracy is compared with other available ab initio computations and experimental results. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Theoretical studies on heats of formation,detonation properties,and bond dissociation energies of monofurazan derivatives

The heats of formation (HOFs) for a series of monofurazan derivatives were calculated by using density functional theory. It is found that the ? CN or ? N₃ group plays a very important role in increasing the HOF values of the furazan derivatives. The detonation velocities and detonation pressures of the furazan derivatives are evaluated at two different levels. The results show that the ? NF₂ group is very helpful for enhancing the detonation performance for the furazan derivatives, but the case is quite the contrary for the ? CH₃ group. An analysis of the bond dissociation energies and bond orders for the weakest bonds indicate that the substitutions of ? CN group are favorable and enhances the thermal stability of the furazan derivatives, but the ? NO₂ groups produce opposite effects. These results provide basic information for the molecular design of novel high‐energy density materials. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Computational studies of bond dissociation energies, ionization potentials, and heat of formation for NH and NH+. Are hybrid density functional theory methods as accurate as quadratic complete basis set and Gaussian-2 ab initio methods?

Ionization potentials, bond dissociation energies, and heat of formation for NH and NH⁺ molecular species as well as for their elements were computed with highly reliable quadratic complete basis set and Gaussian-2 ab initio methods. The results are compared with experimental results and the assurance of these ab initio approaches is assessed. The same studies were also performed with three hybrid density functional methods (B3LYP, B3P86, and B3PW91) in combination with variously sized basis sets. The computational results are discussed in light of density functional theory reliability for exploring the potential energy of small polar molecular systems. Received: 21 July 1997 / Accepted: 8 December 1997     

Theoretical Study of the N-NO2 Bond Dissociation Energies for Energetic Materials with Density Functional Theory

The N-NO2 bond dissociation energies （BDEs） for 7 energetic materials were computed by means of accurate density functional theory （B3LYP, B3PW91 and B3P86） with 6-31G＊＊ and 6-311G＊＊ basis sets. By comparing the computed energies and experimental results, we find that the B3P86/6-311G＊＊ method can give good results of BDE, which has the mean absolute deviation of 1.30kcal/mol. In addition, substituent effects were also taken into account. It is noted that the Hammett constants of substituent groups are related to the BDEs of the N-NO2 bond and the bond dissociation energies of the energetic materials studied decrease when increasing the number of NO2 group.