多溴苊化合物的分子结构和热力学性质

多溴苊是一类潜在的有机污染物。本文采用密度泛函理论在B3LYP/6-311G**水平上优化35个多溴苊化合物的分子几何结构,并获得它们在理想气态的一些热力学性质的数值,研究这些性质与取代的溴原子数目和位置的关系,根据各异构体的标准生成Gibbs自由能的相对大小,求得它们的热力学稳定性顺序。计算结果表明:在大部分多溴苊分子中,除4个氢原子外的其他原子在同一平面上。多溴苊最稳定及最不稳定异构体的ΔfH及ΔfG,都随Br原子数目增加而逐渐增加。溴原子数目相同的多溴苊异构体的ΔfH和ΔfG与溴原子的取代位置有很大的关系,其相对稳定性主要由分子内的处在不同六元环上的邻近Br...Br核排斥作用决定。所有多溴苊化合物在热力学上都比其母体化合物苊相对较难形成。     

多溴代芴的分子结构和热力学性质

多溴代芴化合物是一类潜在的化学污染物,其热力学性质数据对于进一步研究这些化合物的其它物理、化学性质以及它们在环境中的形成、分布及迁移转化机制有重要价值,但这些热力学性质数据极其缺乏.本文采用密度泛函理论在B3LYP/6-311G**水平上优化135个多溴代芴分子的几何结构,并获得它们在理想气态的一些热力学性质的数值,研究这些性质与取代的溴原子数目和位置的关系,根据各异构体的相对标准生成Gibbs自由能的大小,得它们热力学稳定性的顺序.结果表明:多溴代芴分子的几何构型,取决于溴原子的取代位置.多溴代芴最稳定及最不稳定异构体的△fHθ及ΔfGθ,都随Br原子数目增加而逐渐增加.溴原子数目相同的多溴代芴异构体的△fHθ和△fGθ与溴原子的取代位置有很大的关系,其相对稳定性看离域π键和Br…Br核排斥作用的强弱而决定.     

多氯代9,10-菲醌的热力学性质及稳定性的理论研究

采用密度泛函理论(DFT),在B3LYP/6-31G*水平上对135个多氯9,10-菲醌(PCPQ)系列化合物进行全优化和振动分析,得到各分子在298.15K,101.3kPa状态下的热力学参数。设计等键反应,计算了PCPQ系列化合物的标准生成焓(ΔfHθ)和标准生成自由能(ΔfGθ)。用SPSS13.0对这些热力学参数与氯原子的取代位置及取代数目(NPCS)进行多元线性回归,得出相关方程。结果表明:PCPQ系列化合物的Sθ、ΔfHθ和ΔfGθ与NPCS之间有很强的相关性。根据异构体标准生成自由能的相对大小,从理论上求得异构体的相对稳定性。同时,发现氯原子取代模式对扭角(C-C(=O)-C(=O)-C)有很大的影响。     

多溴苊烯化合物的分子结构和热力学性质

多溴苊烯是潜在的一类有机污染物,本文采用密度泛函理论在B3LYP/6-311G**水平上,优化这类化合物的分子几何结构135个,获得它们在理想气态的一些热力学性质的数值,研究这些性质与取代的溴原子数目和位置的关系,根据各异构体的标准生成Gibbs自由能的相对大小,求出它们热力学稳定性的顺序。结果表明:大部分多溴苊烯分子具有平面的几何构型。最稳定及最不稳定异构体的△_fH~θ及△_fG~θ,都随Br原子数目增加而逐渐增加。溴原子数目相同的△_fH~θ和△_fG~θ与溴原子的取代位置有很大的关系,其相对稳定性由分子内Br…Br核排斥作用的强弱而决定。     

多溴代吩噁噻热力学性质的理论计算

采用密度泛函理论方法计算了135个多溴代吩嗯噻在298.15 K和101.325 kPa时其理想气体状态的一些热力学性质的数值;研究这些性质与溴原子取代数目和位置的关系;预测多溴代吩噁噻异构体的相对稳定性.结果表明:多溴代吩嗯噻的热力学性质与溴原子取代数目和位置有良好的相关性,相关系数平方R2值接近1.000;多溴代吩噁噻异构体的相对稳定性主要由能量因素所决定且与多氯代吩嗯噻基本一致;吩噁噻的溴化作用与氯化作用,随卤原子数目的增加在热力学上难易程度的变化情况不同.     

分子拓扑子图编码新方法:估算与预测烷烃热力学函数

在一种新的烷烃分子子图编码方法基础上 ,对烷烃系列 7种热力学函数进行了估计和预测 ,取得了良好结果。对吉布斯自由能ΔGf,原子生成热ΔHatm,气态生成热ΔHf(g) ,液态生成热ΔHf(l) ,热熔Cp,蒸发热ΔHV 和熵S的拟合方程的回归系数分别为 0 9559,1 0 0 0 0 ,0 9965,0 990 5,0 9969,0 9973和 0 992 2。     

粒度对纳米铜与硫酸氢钠反应热力学性质影响的量子化学研究

为了研究纳米粒子的粒度对化学反应热力学性质的影响规律,以球形原子簇来模拟纳米铜颗粒,用量子化学方法(PM6)对不同粒度的铜纳米颗粒与硫酸氢钠反应的热力学性质进行了计算。结果表明:铜原子簇的粒径对其反应热力学的性质有显著的影响,随着铜原子簇的粒径的减小,其标准摩尔反应焓△_rH_m~(?)、标准摩尔吉布斯自由能△_rG_m~(?)、标准摩尔反应熵△_rS_m~(?)减少,而标准平衡常数的对数ln K~(?)增大:并且△_rH_m~(?)、△_rG_m~(?)、△_rS_m~(?)以及ln K~(?)均与粒径的倒数呈较好的线性关系。这些影响规律与实验结果基本一致。     

用理想化学理论对强溶剂化的二元合金系进行活度预测

本文广泛地探讨了利用理想化学理论对强溶剂化的二元合金系进行活度,超额自由能,混合自由能等热力学数据预测的可能性.对15种不同体系进行了计算和预测,它们是:(1)生成单个化合物的二元合金系;(2)生成两个化合物的二元合金系;(3)生成三个化合物的二元合金系;(4)生成四个化合物的二元合金系.本文为从相图获取较多的热力学数据提供了一个有效的方法.当选取合适的模型参数时,计算结果与实验数据吻合很好.     

多氯代二苯并呋喃(PCDFs)光解性质的量子化学研究

多氯代二苯并呋喃(PCDFs)是持久性有机污染物之一，其光化学降解是其主要的环境降解途径，本文是采用量子化学方法对PCDFs光解性质进行研究。本文采取AMl半经验量子化学计算方法计算了所有135种PCDFs的生成热和前线分子轨道能量，据此讨论了PCDFs分子光激发和还原脱氯难易程度与分子结构之间的关系。结果表明生成热可以成功解释PCDFs在水相中随着分子氯取代数目增加而光解速率降低的规律，而前线分子轨道能则可以解释正构烷烃溶剂中随氯原子取代数目增加而还原脱氯在降解机理中越占主导地位的规律，从而从量子化学的角度为实验结果提供了理论解释。     

环己烯催化环氧化反应体系热力学参数计算

本文对所研究的催化环氧化反应体系进行了热力学性质的有关分析,采用Joback基因贡献法估算了反应体系中相关组分的恒压热容、生成热和吉布斯自由能等热力学基础数据,并计算了相关反应的平衡常数,为其工业化生产过程的设计提供了相关基础数据。     

Formation energies of CdSe wurtzoid and diamondoid clusters formed from Cd and Se atomic clusters

Cadmium Selenide thermodynamic formation energies at the molecular and nanoscale range are investigated using density functional theory. The investigation is performed using wurtzoid and diamondoid clusters that represent the wurtzite and zincblende structures at the molecular and nanoscale size range for a cluster number of atoms n ≤ 26. Cd and Se atomic clusters are optimized and used to provide component atomic cluster energies. Although both Cd and Se clusters at the nanoscale have different phases than bulk, the results show that Gibbs free energy, enthalpy, and entropy of formation of CdSe are close to their experimental bulk energies of formation within errors of experimental measurements. CdSe wurtzoids generally have higher absolute (more negative) Gibbs free energy of formation than CdSe diamondoids indicating more stable wurtzoid molecules which is also the case at bulk. The absolute Gibbs free energy of wurtzoids is also higher than experimental value (more negative) because of surface effects at the nanoscale. Enthalpy of formation indicates an exothermic reaction of Cd and Se clusters as is the case at bulk. The entropy of formation of all clusters is size-sensitive and converges towards bulk experimental measurements. Both wurtzoids and diamondoids members contain Cd₁₃Se₁₃ cluster which is the most investigated magic CdSe cluster.     

Conformational analysis of thiopeptides: free energy calculations on the effects of thio-substitutions on the conformational distributions of alanine dipeptides.

When the oxygen atom in a peptide bond is replaced by a sulfur atom, the restriction in the available conformational space and the ability of thioamides to confer resistance to enzymatic degradation renders thioamides as potentially useful building blocks for drug design and protein engineering. The solvation free energy differences between conformers of the same dipeptide can be high. Yet, previous conformational studies, basing on the (phi, psi) conformational energy maps of thio-substituted dipeptides, neglected both explicit water interactions and free energy considerations. In this paper, the (phi, psi) conformational free energy maps are obtained by single umbrella sampling in an explicit water environment for both alanine dipeptide and the corresponding thioamide derivatives. The phi and psi angles for the minima in the relative energy maps calculated with dielectric of 80 are similar to the corresponding phi and psi angles in the relative free energy maps for both Ac-Ala-NHMe (Ac: acetyl; Ala: alanine) and Act-Alat-NHMe (Act: thio-acetyl; Alat: thio-alanine). However, some large differences between the relative energy and relative free energy of major minima indicate that the consideration of free energy is important in determination of the relative occupancy of particular minima. Free energy maps for both Ac-Ala-NHMe and Act-Alat-NHMe show that thio-substitution favors conformations where phi < 0 because of the deeper beta and alphaR minima. The changes in the position and relative stability of minima were explained in terms of the destabilization of the regions near phi = -120, 0 and 120, psi = 60, -60, 180, which correspond to the increased steric hindrance due to the bulkier sulfur atom.     

The Cd–Te phase diagram

The properties of the liquid phase in the Cd–Te system are fit using thermodynamic properties of CdTe(c) recently optimized by the author. These include a high temperature heat capacity significantly lower than commonly used such that the enthalpy of formation of CdTe(c) at its melting point is about 10 kJ/mol less negative than previously thought. An associated solution model with Cd, CdTe, and Te species is used. Seven adjustable parameters are sufficient to quantitatively fit the liquidus and partial pressures of Te₂ and Cd. Additional partial pressures for Te rich CdTe(c) near its melting point are extracted from an earlier study and tabulated. The parameters giving good fits to the liquidus and partial pressures give only a fair fit to the enthalpy of mixing of the liquid phase. Moreover, the parameters giving a good fit to the enthalpy give poor fits to the other data. The sensitivity of the different data types to changes in the interaction parameters of the associated solution model is established. A variation of ±160 J/g atom in the enthalpy parameter determining the CdTe–Te interaction is sufficient to double the fractional standard deviation between experimental and calculated partial pressures of Te₂ over Te rich CdTe(c) from 0.034 to 0.07. Because the degree of association is near its maximum, the measures of fit to the data are insensitive to changes in the parameters determining the Cd–Te interaction.     

Assessment of thermodynamic properties in pure polymers

The thermodynamic properties including enthalpy, entropy and Gibbs free energy of 15 types of pure polymers were derived from experimental data of heat capacity, as a function of temperature. The calculated results are presented in both polynomial expressions and graphs. This database of pure polymers will provide basic parameters in assessments of phase diagrams in binary, ternary and higher-order polymer systems.     

热力学计算软件及其应用

介绍开发热力学计算软件的设计原理、特点及其应用。对用户输入的反应组元进行分子式解析，实现反应式的自动配平，通过调用中扩充的无机化合物热力学数据库对反应进行热力学计算，得到如反应Ｇｉｂｂｓ自由能、反应热力反应平衡常数等基本热力学参数，并将计算结果生成数据文件作为绘图软件的输入。该软件适用于实际体系的热力学计算，用户只需输入反应组元的活度，即可得到反应Ｇｉｂｂｓ自由能变化及气体分压或分压比（若的气体参     

Thermodynamic treamnts of the CaO-SiO2 system

Thermodynamic data for heat capacity, enthalpy, and activity in the CaO-SiO₂ system have been analyzed using the Redlich-Kister formalism with up to six terms. This system shows both liquid-liquid immiscibility and large negative deviations from ideality due to a strong acid base interaction. We have found it necessary to use separate power series treatments for the acidic and basic regions. A number of different mathematical approaches have been previously used for this system, all giving reasonable calculated phase diagrams. Comparisons of the various treatments show major differences in the enthalpy and free energy of mixing. The known thermodynamic properties of CaSiO₃ and Ca₂SiO₄ provide a more reliable test of the accuracy of computer treatments than does the shape of the calculated phase diagram.     

Structure, elastic and thermodynamic properties of the Ni-P system from first-principles calculations

A systematic investigation concerned with the structure, elastic, and finite-temperature thermodynamic properties of Ni₃P, Ni₁₂P₅, Ni₂P, Ni₅P₄, NiP, cubic NiP₂ (C- NiP₂), monoclinic NiP₂ (M- NiP₂), and NiP₃ in the Ni-P system is carried out via first-principles calculations. The elastic stiffness tensors and associated macroscopic elastic properties of these Ni-P compounds including the bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio are calculated. Within the framework of the quasi-harmonic approach, the finite-temperature thermodynamic properties of these Ni-P compounds including the Helmholtz free energy, entropy, heat capacity at constant pressure and enthalpy are predicted. The acquired thermodynamic properties are expected to be utilized for the thermodynamic modelling of the Ni-P system.