计算多氯代烷烃异构体生成焓的新方法

在我们提出诱导极性叠加原理并用以解释同分异构体稳定性及设计烷烃异构体标准生成焓计算新方法的基础上,进一步设计了含多个杂原子体系的取代烷烃——氯代烷烃异构体生成焓的五参数的新方法.与目前应用较广的九参数的基团加和法相比,计算精度高、预报性好,其预报的均方根误差、平均误差比实验数据的相应偏差还要小.而且,特别重要的是,由于所用的参数少,它在理论上可以推广到含各种杂原子或基团以及多种杂原子或基团共存的化合物生成焓的计算.     

计算烷烃异构体生成焓的新方法

基于作者提出的诱导极性叠加原理,设计了包括与诱导极性叠加总量要关的能量项的烷烃异构体的标准生成焓估算的新方法。与前人方法比较,它具有较高的计算精度,较少的参数,各参数物理意义明确,而且理论上可以推广到含多种杂原子的衍生物的标准生成焓的计算。     

烷烃电离能和生成焓的相关性

根据化合物形成过程中价电子能量变化与生成焓之间的关系, 推导出烷烃的生成焓和电离能之间的关系. 以21个烷烃化合物为模型将实验测定的电离能与标准生成焓进行直接关联, 证实了模型方程的适用性, 所得回归方程的相关系数达到0.9999, 估算值与实验值之间的标准偏差仅为0.03 eV. 同时还利用实验测定的标准生成焓对一系列烷烃的电离能作了预测.     

双（2,2-二硝基丙基）甲缩醛的结构和爆轰性能的量子化学研究

利用B3LYP/6-311＋G（2d,p）方法对一种新型含能增塑剂双（2,2-二硝基丙基）甲缩醛进行几何优化,计算了其红外光谱、生成焓和爆轰特性. 分析了最弱键的键离解能和键级并预测了目标化合物的热稳定性. 结果表明双（2,2-二硝基丙基）甲缩醛中的四个N-NO2键的键离解能都为164.38 kJ/mol. 表明目标化合物是一个热力学性能稳定的化合物. 以凝聚相生成焓和分子密度为基础,采用Kamlet-Jacobs方法预测其爆速和爆压. 目标化合物的晶体结构属于P21空间群.     

烃类化合物碳氢键解离焓的密度泛函理论研究

通过比较10种密度泛函方法对烃类化合物碳氢键解离焓的计算精度, 发现新型密度泛函BMK方法具有最高的计算精度. 利用该方法计算了包含饱和链烃,、不饱和链烃、脂环烃和芳香烃在内的172个烃类化合物的碳氢键解离焓,计算均方根误差仅为7.95 kJ•mol^－1, 线性拟合常数为0.985. 通过自然键轨道法分析发现, 烃类物质的碳氢键解离焓与母体的碳氢键杂化轨道成分p%, 自由基奇电子轨道杂化成分p%及自由基的自旋密度三个参数之间存在较好的定量关系. 此外, 饱和链烷烃及不饱和链烃的碳氢键解离焓与碳氢键键长之间也存在较好的线性关系.     

烷烃的热力学性质与结构的关系

在分子图邻接矩阵的基础上提出了一个新的连接性指数mX,mX与烷烃的标准熵、原子化焓、标准生成焓、汽化焓、标准生成吉布斯自由能具有良好的线性关系,相关系数均在0·99以上。结果表明,该模型简单、实用、可靠,而且物理意义明确,对有机物有较高的结构区分能力。对157种烷烃的计算结果表明,热力学性质的计算值和实验值的平均相对误差不超过0·77%。     

取代烷烃极性交替规律的进一步探讨

运用 Ｇ９４Ｗ量子化学程序包,在 ＨＦ／６－３１＋ Ｇ基组和全几何优化的水平上,对一系列烷烃及其取代烷烃分子进行从头计算．通过比较母体烷烃及取代烷烃中原子的电荷,进一步证实并具体阐述取代烷烃有如共轭体系那样也存在极性交替规律．并着重提出了诱导极性有向叠加的观点,探讨其在定性分析键型相同的同分异构体稳定性等方面的应用．     

新型高能量密度化合物3,6-双(3,5-二硝基-1,2,4-三唑-1)-1,2,4,5-四嗪-1,4-二氧化物的性能预估及合成路线设计

采用C++自编译程序及组合原理,设计并筛选出一种未见报道的新型富氮类高能量密度化合物-3,6-双(3,5.二硝基.1,2,4-三唑.1)-1,2,4,5-四嗪-1,4-二氧化物,用B3LYP法,在6-31G**基组水平上得到该化合物全优化构型;在振动分析的基础上求得体系的振动频率、IR谱;通过键级分析得到热解引发键的键离解能(BDE);采用Monte-Carlo 方法预估了密度;设计等键等电子反应计算了生成焓;运用Kamlet-Jacobs公式预测爆速、爆压和爆热;运用Keshavarz 等推导的预估撞击感度H50的公式预测了撞击感度性能;并利用逆合成分析法设计其合成路线.结果表明:该化合物存在8个强吸收峰,校正后的热解引发键的BDE为264KJ·mol-1,稳定性较优;密度1.955 g·cm-3、生成焓901.72 kJ·mol-1、爆速9191.48 m·s-1、爆压39.32 GPa、爆热6705.15 j·g-1;撞击感度H50为55.85cm,低于黑索金(RDX)和奥克托今(HMx);以上性能均达到了高能量密度化合物的标准,且该化合物设计合成路线步骤较少、原料易得,有望得到广泛应用.     

3,7-二硝亚胺基-2,4,6,8-四硝基-2,4,6,8-四氮杂双环[3.3.0]辛烷结构与性能的量子化学研究

设计了一种新型高能量密度化合物--3,7-二硝亚胺基-2,4,6,8-四硝基-2,4,6,8-四氮杂双环[3.3.0]辛烷, 应用密度泛函理论(DFT)的B3LYP 方法在6-31G(d,p)基组水平上对该化合物进行了结构全优化, 并计算得到其红外(IR)光谱; 通过键级分析获得热解引发键的位置为N7-N22, 同时求得校正后的键离解能为91.47 kJ/mol. 采用Monte-Carlo方法预测该化合物的理论密度为2.16 g/cm³; 基于理论密度并结合等键反应及Kamlet-Jacobs公式预测了生成焓、爆速、爆压和爆热值分别为1219.94 kJ/mol, 10.43 km/s, 53.44 GPa和7407.84 J/g. 以上性能参数显示, 该目标化合物达到了高能量密度化合物的基本要求, 是一种潜在的含能材料. 同时给出了该化合物的逆合成路线.     

高效液相色谱喹啉醚基键合硅胶固定相的制备及评价

采用固液相连续反应法,以γ-环氧丙氧基)丙基三甲氧基硅烷(KH560)为偶联剂,制备了一种喹啉醚基键合硅胶固定相(QBS),采用元素分析、漫反射红外光谱和热分析表征了固定相的结构。多种溶质为探针(包括非极性的烷基苯和多环芳烃、芳香族化合物位置异构体及极性的核苷和碱基等),较系统地研究了该新固定相的色谱性能。研究表明,新固定相与ODS相比,除具有弱的疏水性外,还能与溶质发生多种作用,如：氢键和π-π作用等。在分离非极性的多环芳烃时主要基于疏水作用;在分离极性的核苷和碱基时,氢键和络合作用较重要;在分离芳香族化合物位置异构体时,溶质极性取代基与喹啉醚基键合相的氢键作用。溶质苯环与喹啉基配体之间的π-π作用,两协同作用提高了QBS对位置异构体的分离选择性。     

Additivity methods for prediction of thermochemical properties. The Laidler method revisited. 2. Hydrocarbons including substituted cyclic compounds

A revised parameterization of the extended Laidler method for predicting standard molar enthalpies of atomization and standard molar enthalpies of formation at T = 298.15 K for several families of hydrocarbons (alkanes, alkenes, alkynes, polyenes, poly-ynes, cycloalkanes, substituted cycloalkanes, cycloalkenes, substituted cycloalkenes, benzene derivatives, and bi and polyphenyls) is presented. Data for a total of 265 gas-phase and 242 liquid-phase compounds were used for the calculation of the parameters. Comparison of the experimental values with those obtained using the additive scheme led to an average absolute difference of 0.73 kJ · mol⁻¹ for the gas-phase standard molar enthalpy of formation and 0.79 kJ · mol⁻¹ for the liquid-phase standard molar enthalpy of formation. The database used to establish the parameters was carefully reviewed by using, whenever possible, the original publications. A worksheet to simplify the calculation of standard molar enthalpies of formation and standard molar enthalpies of atomization at T = 298.15 K based on the extended Laidler parameters defined in this paper is provided as supplementary material.     

An Electrostatic Bond Energy Model for Enthalpies of Formation of Chloroalkanes in Gaseous States

An electrostatic bond energy model is formulated to fit the enthalpies of formation and dipole moments of the alkanes and chloroalkanes. In this model, the charge distributions are calculated by an electrostatic approach similar to the "MSE" method, and the enthalpy of formation of a molecule is the sum of the bond energy terms plus the electrostatic energy of the interactions between the charges on all atoms. All parameters of this model are obtained by parameterization. The calculated dipole moments for 13 chloroalkanes and enthalpies of formation for 19 alkanes and non-geminal chloroalkanes agree with the determined values very well. To calculate the enthalpies of formation of geminal chloroalkanes, a correction mainly attributed to the van der Waals interactions in the geminal substituted group, about 24 kJ/mol per pair of geminal chlorine atoms, is introduced.     

Theoretical study of the enthalpies of formation for C40H56 carotenes

Theoretical study of the enthalpies of formation (DeltaHf) for polyenes up to nine ethylene units and for several C40H56 carotenes including beta-carotene, alpha-carotene, lycopene, and prolycopene is presented. For polyenes and small branched alkenes, we used G2, G3, and G3MP2B3 theories, and the DeltaHf values were evaluated with the atomization, isodesmic bond separation, and homodesmic schemes. The applicability of six DFT functionals were evaluated by comparing their predictions with those obtained using G3 theory within the atomization scheme. Additivity approaches, including atom equivalents and group equivalents using DFT and semiempirical theories, were explored. We found that group equivalents associated with isodesmic reactions are able to provide the most accurate predictions within the test set. The predictions from the six functionals are in good agreement with the G3 results. Among them, B3LYP performs the best, with an average absolute deviation of only 0.30 kcal/mol. The application of DFT in the prediction for the DeltaHf value of C40H56 carotenes is promising.     

Aromaticity and stability going in opposite directions: An energetic,structural, magnetic and electronic study of aminopyrimidines

The relation between molecular energetics and aromaticity was investigated for the interaction between the amino functional group and the nitrogen atoms of the pyridine and pyrimidine rings, using experimental thermodynamic techniques and computational geometries, enthalpies, chemical shifts, atomic charges and the Quantum Theory of Atoms in Molecules. 2,4-diaminopyrimidine and 2,4,6-triaminopyrimidine were studied by static bomb combustion calorimetry and Knudsen effusion technique. The derived gaseous-phase enthalpies of formation together with the enthalpies of formation of the three isomers of aminopyridine reported in the literature, were compared with the calculated computationally ones and extended to other diamino- and triaminopyrimidine isomers using the MP2/6-311++G(d,p) level of theory.The results were analyzed in terms of enthalpy of interaction between substituents and, due to the absence of meaningful stereochemical hindrance, strong inductive effects, or intramolecular hydrogen bonds according to QTAIM results, the resonance electron delocalization plays an almost exclusive role in the very exothermic enthalpies obtained. Therefore, this enthalpy of interaction was used as an experimental energetic measure of resonance effects and analyzed in terms of aromaticity. It was found that more conjugation between substituents means less aromaticity according to the magnetic (NICS) and electronic (Shannon) criteria, but more aromaticity according to the geometric (HOMA) criterion.     

A New Generalized Bond Energy/Group Contribution Scheme for Calculating the Standard Heat of Formation of Monomers and Polymers. Part V. Oxygen Compounds

Abstract

The new generalized bond energy scheme has been extended to organic oxygen compounds. About 50 different types of bonds have been identified and their ΔH_f°(g) contributions and atomization energies evaluated by a procedure similar to multilinear regression analysis. Recent thermochemical data (1969-1973) on 145 oxygen compounds and about 80 ring compounds have been employed to test the efficiency of the scheme in predicting the gas phase heats of formation. This was found to be about ±0. 8 kcal/mole, which is quite comparable to the group contribution method of Benson and co-workers involving a much larger number of parameters.

The typical chemical bonds identified and resolved in respect of their bond energies bear good consistency and correlation with bond lengths and force constants measurable independently. Heats of formation and polymerization on about 47 monomer-polymer systems and enthalpies of other polymeric reactions have been predicted and compared with available experimental data.     

Energetics of intra- and intermolecular bonds in ω-alkanediols

The enthalpies of combustion and vaporization at 298.15 K of the-alkanediols were determined with a CRMT rocking calorimeter equipped with a micro-bomb and a Tian-Calvet calorimeter equipped with a Knudsen effusion cell, respectively. The enthalpies of formation in the condensed and gaseous phases and the enthalpies of atomization are calculated. They depend linearly on the number of carbon atoms. Furthermore, the results permit derivation of the enthalpy of an intermolecular hydrogen bond in liquid-alkanediols and calculation of mean enthalpies of the C-C and C-OH bonds. All these thermochemical quantities are discussed in relation to the structural particulars of the molecules.     

Theoretical study on the thermodynamic properties and self-decomposition of methylbenzenediol isomers

Alkylated hydroxylated aromatics are major constituents of various types of fuels, including biomass and low-rank coal. In this study, thermochemical parameters are obtained for the various isomeric forms of methylbenzenediol isomers in terms of their enthalpies of formation, entropies, and heat capacities. Isodesmic work reactions are used in quantum chemical computations of the reaction enthalpies for O-H and H?C-H bond fissions and the formation of phenoxy- and benzyl-type radicals. A reaction potential energy on the singlet-state surface surface is mapped out for the unimolecular decomposition of the 3-methylbenzene-1,2-diol isomer. According to the calculated high pressure-limit reaction rate constants, concerted hydrogen molecule elimination from the methyl group and the hydroxyl group, in addition to intermolecular H migration from the hydroxyl group, dominates the unimolecular decomposition at low to intermediate temperatures (T ≤ 1200 K). At higher temperatures, O-H bond fission and concerted water elimination are expected to become the sole decomposition pathways.     

Automatic estimation of heats of atomization and heats of reaction

Various additivity schemes for estimating heats of atomization have been evaluated to test their usefulness for designing a computer program. The approach is based on the Allen scheme and uses parameters obtained from thermochemical data. In addition, a method has been developed which allows the direct calculation of reaction enthalpies. Only the immediate environment of the bonds involved in the reaction has to be scanned. A program based on this method utilizes thermochemical parameters, too. Computation times with this program are extremely short and independent of the size of the molecules participating in the reaction. The procedure can be applied to a large variety of organic compounds. Examples demonstrate the accuracy of the predicted values.     

Energetic study of bromobenzonitrile isomers: insights on the intermolecular interactions, aromaticity and electronegativity

The standard (p ^o = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, of 2-, 3- and 4-bromobenzonitrile isomers were calculated from the combination of the following two parameters experimentally determined: the standard molar enthalpy of formation in the condensed phase, derived from the standard molar energy of combustion in oxygen at T = 298.15 K, measured by rotating-bomb combustion calorimetry, and the standard molar enthalpy of sublimation at the same reference temperature, derived from vapour pressure studies at several temperatures, as measured by mass-loss Knudsen effusion. The computational calculations complement the energetic study and analysis of the electron delocalization allows a comparison between the fluorine and bromine benzonitrile isomers. The harmonic oscillator model of aromaticity and nucleus-independent chemical shift aromaticity criteria and the natural bond orbital analysis were applied and related with the intramolecular enthalpic interactions. The intermolecular interactions in the crystal packing were analysed in terms of enthalpic and entropic contributions, using the crystallographic structures available in literature.