Theoretical Study on Intermolecular Interactions and Thermodynamic Properties of Nitroamine Dimers

Ab initio self-consistent field(SCF) and Mφller-Plesset correlation correction methods employing 6-31G^** basis set have been applied to the optimizations of nitroamine dimers.The binding energies have been corrected for the basis set superposition error (BSSE) and the zero-point energy.Theree optimized dimers have been obtained.The BSSE corrected binding energy of the most stable dimer is predicted to be -31.85kJ/mol at the MP4/6-31G^**//MP2/6-31G^** level.The energy barriers of the Walden conversion for -NH2 group are 19.7kJ/mol and 18.3kJ/mol for monomer and the most stable dimer,respectively.The molecular interaction makes the internal rotation around N1-N2 even more difficult.The thermodynamic properties of nitroamine and its dimers at different temperatures have been calculated on the basis of vibrational analyses.The change of the Gibbs free energy for the aggregation from monomer to the most stable dimer at standard pressure and 298.2 K is predicted to be 14.05kJ/mol.     

Conformers and intramolecular hydrogen bonding of the oxalic acid monomer and its anions

Density functional theory, B3LYP/6‐31G** and B3LYP/6‐311+G(2d,p), and ab initio MP2/6‐31G** calculations have been carried out to investigate the conformers, transition states, and energy barriers of the conformational processes of oxalic acid and its anions. QCISD/6‐31G** geometrical optimization is also performed in the stable forms. Its calculated energy differences between the two most stable conformers are very near to the related observed value at 7.0 kJ/mol. It is found that the structures and relative energies of oxalic acid conformers predicted by these methods show similar results, and that the conformer L1 (C_2h) with the double‐interfunctional‐groups hydrogen bonds is the most stable conformer. The magnitude of hydrogen bond energies depends on the energy differences of various optimized structures. The hydrogen bond energies will be about 32 kJ/mol for interfunctional groups, 17 kJ/mol for weak interfunctional groups, 24 kJ/mol for intra‐COOH in (COOH)₂, and 60 kJ/mol for interfunctional groups in (COOH)COO⁻¹ ion if calculated using the B3LYP/6‐311+G(2d,p) method. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 76: 541–551, 2000     

Examination of formamide,formamidic acid,amidine dimers,and the double proton transfer transition states involving these dimers

Structures and relative energies were obtained for the hydrogen bonded dimers of formamide and formamidic acid using the 3-21G basis set. A double proton transfer transition state is claimed to link these two dimers. While the structure of the transition state was intermediate between those of the two dimers, the energy was only 7.6 kJ/mol greater than the less stable formamidic acid dimer. The activation energy from the formamide dimer side of the reaction was found to be 125 kJ/mol of dimer. A similar transition state was found for the amidine dimer system. The activation energy for this model reaction was found to be 66.9 kJ/mol of dimer.     

Theoretical Study on the Intermolecular Interactions of Tetrazole Dimers

1 INTRODUCTION Tetrazole and its derivatives are widely applied in the fields of agriculture, biology, chemistry, phar- macology and photographic technology, and they play significant roles in the science and technology as well as national defence[1]. In the past, the res- earches were focused on the molecular geometries, electronic structures, IR, thermodynamic properties, tautomerization, pyrogenation and sensitivity of tetrazole compounds[1～5]. However, study of tetra- zole dimers ha…     

Theoretical Study on the Intermolecular Interactions between 1,1‐Diamino‐2,2‐Dinitroethylene and H2O

The density functional method was applied to the study of 1,1‐diamino‐2,2‐dinitroethylene (Fox‐7)/H₂O dimer. All the possible dimers ( 1, 2 and 3 ), as well as the monomers, were fully optimized with the DFT method at the B3LYP/6‐311++G^** level. The basis set superposition errors (BSSE) are 4.62, 4.07 and 3.45 kJ/mol, and the zero point energy (ZPE) corrections for the interaction energies are 7.94, 5.66 and 6.40 kJ/mol for 1, 2 and 3 , respectively. Dimer 1 is the most stable, judged by binding energy. After BSSE and ZPE corrections, the greatest corrected intermolecular interaction energy of dimer 1 was predicted to be ?29.36 kJ/mol. The charge redistribution mainly occurs on the adjacent N–H··· O atoms and N–O··· H atoms between submolecules. The oxygen in the nitro group acts as a moderate hydrogen acceptor as compared to water oxygen. Based on the statistical thermodynamic method, the standard thermodynamic functions, heat capacities (C⁰_P), entropies (S⁰_T) and thermal corrections to enthalpy (H⁰_T), and the changes of thermodynamic properties on going from monomer to dimer over the temperature range 200.00‐700.00 K were predicted. It is energetically or thermodynamically favorable for Fox‐7 to bind with H₂O and to form dimer 1 at room temperature.     

叠氮乙烷二聚体分子间相互作用的理论研究

Energetic materials are aggregative and mixed systems. The intermolecular interactions play significantroles in the physical,chemical and explosive property. The study on intermolecular interactions of energetic materials has attracted wide attention. The organic azides are an important category of energetic materials and widely used in many fields. Ethyl azide is the simple model having the explosive property for the organic azides energetic compound. Ethyl azide monomer（Ⅰ）and all its possible stable clusters（Ⅱ,Ⅲ and Ⅳ）are fully optimized by ab initio method at the HF/6-311++G** level. Vibrational frequencies calculated to ascertain each structure are characterized to be the stable structure（no imaginary frequencies）. The proportions of correlated interaction energies to their total interaction energies ΔE（MP2）are 65.14%,63.76% and 65.62% for Ⅱ,Ⅲ and Ⅳ respectively. In addition,the basis set superposition error（BSSE）correction energies are 7.82,7.61 and 4.40 kJ/mol for Ⅱ,Ⅲ and Ⅳ respectively. The zero point energy （ZPE） corrections for the interaction energies are much less than those of MP2 electron correlation and BSSE correction energies. After MP2 electron correlation correction,BSSE and ZPE correction,the greatest corrected intermolecular interaction of the dimers is -10.45 kJ/mol. The charge redistribution mainly occurs on the adjacent N?H atoms between submolecules. The charge transfer between two subsystems is very small. Natural bond orbital（NBO）analysis is performed to reveal the origin of the interaction. Based on the statistical thermodynamic method,the standard thermodynamic functions,heat capacities（C0p）,entropies（S0m）and enthalpies（H0m）and the changes of thermodynamic properties from the monomer to dimer with the temperatures ranging from 200. 00 K to 800. 00 K have been obtained.     

6-甲基-4-羟基嘧啶单体及二聚体质子转移过程的理论研究

应用密度泛函理论的B3LYP/6-311+G(d)方法研究了6-甲基-4-羟基嘧啶单体及二聚体质子转移的异构化反应.对反应势能面的研究发现,该化含物可能存在9种单体异构体,对其最稳定的单体构型进行分析.各单体间异构化反应的过渡态共有9种,反应的活化能最小为22.06 kJ/mol,最大为356.55 kJ/mol,最可能的反应路径在室温下即可进行. 研究了2种二聚体及其异构化反应的过渡态,发现二聚体均比其对应的单体稳定,而且质子转移所需要的活化能仅为20.13 kJ/mol,比单体低很多. 氢键在这种变化中起了主要作用,由单体和二聚体的总能量计算了氢键的键能.     

NTO二聚体分子间相互作用的理论研究

在DFT-B3LYP/6-311＋＋G**水平上求得NTO二聚体势能面上六种优化构型和电子结构. 经基组叠加误差(BSSE)和零点能(ZPE)校正, 求得分子间最大相互作用能为－53.66 kJ/mol. 二子体系间的电荷转移很少. 由自然键轨道分析揭示了相互作用的本质. 对优化构型进行振动分析, 并基于统计热力学求得200.0～800.0 K温度范围从单体形成二聚体的热力学性质变化. 发现二聚主要由强氢键所贡献, 但结合能大小并不为氢键所完全决定. 二聚过程在较低温度或常温下能自发进行.     

Structure of a C26H28 alkene formed via titanium-promoted reductive dimerization of 4-(spirocyclopropyl)-pentacyclo[5.4.0.02,6.03,10.05,9]undecan-8-one

A spiro-fused C₂₆H₂₈ cage≓ dimer hydrocarbon contains two three-membered rings, two four-membered rings, eight five-membered rings, and two six-membered rings. The molecule is calculated by molecular mechanics to have 902 kJ/mol of strain energy distributed primarily between angle strain (457 kJ/mol) and torsional interactions (368 kJ/mol). Molecular mechanics calculations and a geometry-optimized ab initio calculation are used to analyze the bond lengths and bond angles in the molecule. There is one major discrepancy between observed and calculated distances.     

1H-ANTA二聚体分子间相互作用的密度泛函理论研究

在DFT-B3LYP/6-311＋＋G**水平上求得1H-3-硝基-5-氨基-1,2,4-三唑(1H-ANTA)二聚体势能面上5种优化构型和电子结构. 经基组叠加误差(BSSE)和零点能(ZPE)校正, 求得分子间最大结合能为70.63 kJ/mol. 二聚体的形成使电荷向三唑环转移. 由氢键强弱推断二聚体稳定性的顺序与结合能顺序相一致, 氢键是二聚体的主要作用形式. 对优化构型进行振动分析, 并基于统计热力学求得200.0～800.0 K温度范围内单体形成二聚体的热力学性质变化. 发现在该温度范围所有二聚过程均能自发进行.     

Density functional theory (DFT) and ab initio investigations of the electronic and molecular structures of the monomer and the dimer of trimethylaluminium

The electronic and molecular structures of the monomer and dimer of trimethylalu-minium have been studied using density functional theory and ab initio MP2 method. The optimized geometry of the monomer Al(CH3)3 is of C3h symmetry, whereas that of the dimer [A1(CH3)3]2 contains a carbon-bridged four-membered ring structure with C2h symmetry. The hydrogen-bridged six-membered ring structure is found to be unstable. The calculated dimerization energy for the four-membered ring structure is 78 kJ/mol, in close proximity to the experimental value of 85.27 kJ/mol.     

金属丝桃蒽酮结构变化的理论研究

用MMX和AM1方法对金属桃蒽酮(HYP)结构变化过程的生成热进行了计算.发现:1.HYP1,2位OH可越过20kJ/mol左右的势,绕C--O键旋转而形成分子内氢键,并估算出键能约为10kJ/mol;2.HYP其他四个OH也可进行类似的构象变化,势垒在26kJ/mol左右,相应分子内氢键键能约为20kJmol;3.HYP分子内氢传递产生的异构体在能量上不稳定,进而在基础上探讨了1,2位OH分子内氢键的形成对HYP光敏活性的影响。     

HSCCS自由基势能面的理论研究

在CCSD(T)/6-311G(d,f)//MP2/6-311G(d,f) ZPE水平下,计算得到含有8个异构体和11个过渡态的HSCCS自由基体系势能面,讨论了异构体的结构与稳定性及异构体之间的异构化过程.结果表明异构体m1的能量最低,除m1以外,异构体m2和m3的能量也比较低,在MP2水平上,过渡态TS1的能量比异构体m2仅高3.9kJ/mol,而在CCSD(T)水平上,TS1的能量比m2低14.6 kJ/mol,这说明异构体m2可以迅速转化为能量更低的m1.异构体m3的能量比异构体m1高49.99 kJ/mol,可以推断,在合适的实验条件下可以观测到异构体m1.     

硝酸乙酯分子间相互作用的ab initio研究

在abinitio-HF/6-31G水平上求得硝酸乙酯二聚体势能面上的四种优化构型和电子结构。经MP2电子相关校正和基组叠加误差(BSSE)以及零点能(ZPE)校正，求得二聚体的最大结合能为11.46kJ.mol^-^1，还进行HF/6-311G和HF/6-311++G水平的总能量比较计算，发现6-31G基组对计算结合能比较适合，二子体系间的电荷转移很少，对优化构型进行振动分析，并基于统计热力学求得从单体形成二聚体的热力学性质变化。     

Decomposition reaction rate of BCl3-C3H6(propene)-H2 in the gas phase

The decomposition reaction rate in the BCl(3)-C(3)H(6)-H(2) gas phase reaction system in preparing boron carbides was investigated based on the most favorable reaction pathways proposed by Jiang et al. [Theor. Chem. Accs. 2010, 127, 519] and Yang et al. [J. Theor. Comput. Chem. 2012, 11, 53]. The rate constants of all the elementary reactions were evaluated with the variational transition state theory. The vibrational frequencies for the stationary points as well as the selected points along the minimum energy paths (MEPs) were calculated with density functional theory at the B3PW91/6-311G(d,p) level and the energies were refined with the accurate model chemistry method G3(MP2). For the elementary reaction associated with a transition state, the MEP was obtained with the intrinsic reaction coordinates, while for the elementary reaction without transition state, the relaxed potential energy surface scan was employed to obtain the MEP. The rate constants were calculated for temperatures within 200-2000 K and fitted into three-parameter Arrhenius expressions. The reaction rates were investigated by using the COMSOL software to solve numerically the coupled differential rate equations. The results show that the reactions are, consistent with the experiments, appropriate at 1100-1500 K with the reaction time of 30 s for 1100 K, 1.5 s for 1200 K, 0.12 s for 1300 K, 0.011 s for 1400 K, or 0.001 s for 1500 K, for propene being almost completely consumed. The completely dissociated species, boron carbides C(3)B, C(2)B, and CB, have very low concentrations, and C(3)B is the main product at higher temperatures, while C(2)B is the main product at lower temperatures. For the reaction time 1 s, all these concentrations approach into a nearly constant. The maximum value (in mol/m(3)) is for the highest temperature 1500 K with the orders of -13, -17, and -23 for C(3)B, C(2)B, and CB, respectively. It was also found that the logarithm of the overall reaction rate and reciprocal temperature have an excellent linear relationship within 700-2000 K with a correlation coefficient of 0.99996. This corresponds to an apparent activation energy 337.0 kJ/mol, which is comparable with the energy barrier 362.6 kJ/mol of the rate control reaction at 0 K but is higher than either of the experiments 208.7 kJ/mol or the Gibbs free energy barrier 226.2 kJ/mol at 1200 K.     

基于平均影响值的反向传播神经网络方法用于提高密度泛函理论计算Y—NO键均裂能精度

将基于平均影响值(Mean impact value,MIV)的反向传播神经网络(Back propagation neural netowrk,BPNN)(MIV-BPNN)方法用于提高密度泛函理论(Density functional theory,DFT)计算Y—NO(Y=N,S,O及C)键均裂能的精度.利用量子化学计算和MIV-BPNN联合方法计算92个含Y—NO键的有机分子体系的均裂能.结果表明,相对于单一的密度泛函理论B3LYP/6-31G(d)方法,利用全参数下的BPNN方法计算92个有机分子均裂能的均方根误差从22.25 kJ/mol减少到1.84 kJ/mol,而MIV-BPNN方法使均方根误差减少到1.36 kJ/mol,可见B3LYP/6-31G(d)和MIV-BPNN联合方法可以提高均裂能的量子化学计算精度,并可预测实验上无法获取的均裂能值.     

甲醛与乙醛,甲醚,硝基甲烷相互作用的从头算研究

用6-31G、全构型优化,研究了甲醛与乙醛、甲醚、硝基甲烷的相互作用。结果表明所有超分子稳定构型都包含2个C—H—O氢键的平面环状结构。H—O距离为0.228～0.264 nm,作用能为—19～—24 kJ/mol,与二聚水的作用能接近。稳定性主要取决于甲基上取代基Y吸电子能力以及环状结构中氢键张力。STO-3G不很适用于研究这类分子的相互作用。     

Activation energy for the disproportionation of HBrO2 and estimated heats of formation of HBrO2 and BrO2

The kinetics of the reaction HBrO(2) + HBrO(2) --> HOBr + BrO(3)(-) + H(+) is investigated in aqueous HClO(4) (0.04-0.9 M) and H(2)SO(4) (0.3-0.9 M) media and at temperatures in the range 15-38 degrees C. The reaction is found to be cleanly second order in [HBrO(2)], with the experimental rate constant having the form k(exp) = k + k'[H(+)]. The half-life of the reaction is on the order of a few tenths of a second in the range 0.01 M < [HBrO(2)](0) < 0.02 M. The detailed mechanism of this reaction is discussed. The activation parameters for kare found to be E(double dagger) = 19.0 +/- 0.9 kJ/mol and DeltaS(double dagger) = -132 +/- 3 J/(K mol) in HClO(4), and E(double dagger) = 23.0 +/- 0.5 kJ/mol and DeltaS(double dagger) = -119 +/- 1 J/(K mol) in H(2)SO(4). The activation parameters for k' are found to be E(double dagger) = 25.8 +/- 0.5 kJ/mol and DeltaS(double dagger) = -106 +/- 1 J/(K mol) in HClO(4), and E(double dagger) = 18 +/- 3 kJ/mol and DeltaS(double dagger) = -130 +/- 11 J/(K mol) in H(2)SO(4). The values Delta(f)H(29)(8)(0)[BrO(2)(aq)] = 157 kJ/mol and Delta(f)H(29)(8)(0)[HBrO(2)(aq)] = -33 kJ/mol are estimated using a trend analysis (bond strengths) based on the assumption Delta(f)H(29)(8)(0)[HBrO(2)(aq)] lies between Delta(f)H(29)(8)(0)[HOBr(aq)] and Delta(f)H(29)(8)(0)[HBrO(3)(aq)] as Delta(f)H(29)(8)(0)[HClO(2)(aq)] lies between Delta(f)H(29)(8)(0)[HOCl(aq)] and Delta(f)H(29)(8)(0)[HClO(3)(aq)]. The estimated value of Delta(f)H(29)(8)(0)[BrO(2)(aq)] agrees well with calculated gas-phase values, but the estimated value of Delta(f)H(29)(8)(0)[HBrO(2)(aq)], as well as the tabulated value of Delta(f)H(29)(8)(0)[HClO(2)(aq)], is in substantial disagreement with calculated gas-phase values. Values of Delta(r)H(0) are estimated for various reactions involving BrO(2) or HBrO(2).     

3,6-二羟基哒嗪质子转移过程的理论研究

为了探索3,6-二羟基哒嗪分子醇式和酮式结构互变异构化的反应机理,本研究组采用DFT B3LYP/6-311+G(d)方法对标题化合物异构化反应的势能面进行了研究,在探讨各种可能的反应途径中,发现至少有34种异构体和43种过渡态.结果表明,6-羟基-3(2H)-哒嗪酮不论是单体,与水形成配合物,还是二聚体,比其相对应的异构体能量低,表明在通常情况下是以6-羟基-3(2H)-哒嗪酮形式稳定存在的,这与前人通过实验数据对互变异构体的比率进行预测的结果是一致的;在考察的可能反应途径中,直接进行的分子内质子转移过程需要的活化能为142.2 kJ·mol^-1,水助催化时,反应活化能为41.3 kJ·mol^-1,考虑溶剂效应后,其活化能为59.2 kJ·mol^-1,二聚体双质子转移的活化能为16.8 kJ·mol^-1,二聚体双质子转移所需活化能最低,在室温下就可以进行.由此可见氢键在降低反应活化能方面起着重要的作用.     

分子筛催化cis-2-丁烯的双键异构反应机理的DFT研究

基于含有两个Si和一个Al的分子筛3T簇模型, 利用密度泛函方法(DFT)研究了分子筛催化1-丁烯双键异构为cis-2-丁烯的反应机理. 在B3LYP/6-31G(d,p)计算水平上对反应各驻点进行了全优化, 并计算了反应的活化能. 研究发现, 分子筛上的酸性OH基团首先通过物理吸附靠近1-丁烯的双键, 形成了π配位复合物后, 丁烯双键的端基C原子逐渐抽取这个质子, 同时相邻酸性位的一个O原子也抽取丁烯碳链上的一个H原子, 形成吸附态的cis-2-丁烯, 最后通过脱附形成产物, 使分子筛复原, 反应按照协同反应机理发生. 计算得到的表观活化能是55.9 kJ/mol, 与实验结果接近.