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.     

计算饱和醇异构体标准生成焓的新方法

基于极性叠加原理,在成功设计烷烃异构体和多氯代烷烃生成焓计算新方法的基础上,设计了一种计算多元醇异构体生成焓的新方法,并合理地假定任一异构体的原子化焓等于三种键(C-C、C-H和C-O-H键)的键能、极性叠加能项以及氢键能项的加和.用这一模型拟合24种原子化焓数据,得到了标准生成焓的估算公式.为了检验预测的精确性,又设计了一种预测方法,使用在排除被预测的化合物条件下回归得到的参数,预测该化合物的生成焓.按这种方法,预测了24种异构体的生成焓.通过该5参数预测的相对于实验值的各种误差(平均绝对误差、均方根误差和最大绝对误差)不仅比7参数的基团法预测的对应误差小得多,而且比相应实验数据的误差还要小.与键加和法比较,该方法的模型包含了极性叠加能和氢键能量,该两项代表了主要的非键相互作用能,表征了不同异构体的结构差异,并大大减少了参数.     

碳酸盐标准生成焓的计算

碳酸盐标准生成焓的计算戴长文，王振民，徐琰，戴晓弘（郑州大学化学系，郑州，４５００５２）（郑州高新技术开发区，郑州，４５０００１）关键词热力学性质，标准生成焓，碳酸盐预测无机化合物生成热的计算方法已见报道［１，２］，但引入经验参数过多，且计算偏差亦较...     

诱导效应指数与XSiRxH3—x的标准生成热

诱导效应指数与ＸＳｉＲｘＨ３－ｘ的标准生成热张秀利（河北轻化工学院基础部石家庄０５００１８）关键词诱导效应指数标准生成热键裂能烷基硅衍生物对于含硅有机物的标准生成热大多未见报导［１－２］，本文将利用诱导效应指数Ｉ［３，４］，作为参数，建立一套简单而准...     

三元配合物Tm[(C_5H_8NS_2)_3(C_(12)H_8N_2)]的热化学性质研究

在无水乙醇中,用吡咯烷二硫代氨基甲酸铵(APDTC)和1,10-邻菲咯啉(o-phen·H2O)与TmCl3·3.65H2O作用,合成了未见文献报道的三元固态配合物,确定它的组成为Tm[(C5H8NS2)3(C12H8N2)]。用RD496-Ⅲ微量热计测定了298.15K下水合氯化铥及两个配体在无水乙醇中的溶解焓,两个配体醇溶液的混合焓及不同温度下标题化合物液相生成反应的焓变。在实验和计算基础上,得到了液相生成反应的热力学参数(活化焓、活化熵和活化自由能),速率常数和动力学参数(表现活化能、频率因子和反应级数)。通过合理的热化学循环,求得了298.15K时标题化合物的固相生成反应焓变;推导了用该热量计测定固态物质比热容的计算式,并测定了题目配合物298.15K的比热容。用RBC-Ⅱ精密转动弹热量计测定了题目配合物的恒容燃烧热,计算了它们的标准摩尔燃烧焓和标准摩尔生成焓。     

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%。     

氯化烷基咪唑系列离子液体标准摩尔燃烧焓和生成焓

用精密氧弹热量计测定了4种离子液体: 氯化1-甲基-3-乙基咪唑(C2MIC), 氯化1-甲基-3-丁基咪唑(C4MIC), 氯化1-甲基-3-戊基咪唑(C5MIC)和氯化1-甲基-3-己基咪唑(C6MIC)的燃烧热, 计算了它们的标准摩尔燃烧焓 和标准摩尔生成焓 , 结合文献中的标准摩尔溶解焓, 估算了烷基咪唑阳离子在水溶液中的标准摩尔生成焓, 以及亚甲基对标准摩尔燃烧焓和标准摩尔生成焓的贡献.     

诱导效应指数的量子化学研究

蒋明谦等曾提出了一种计算诱导效应指数的方案,用于讨论非共轭化合物.这种计算方案在蒋明谦的另一本专著中,又得到了进一步的推广.与过去一般都是以成键元素电负性差值来估计键极性的方法不同,诱导效应指数是用各原子的电负性分数来估计一个共价键上极性状态的.计算这种指数的基础是这种基团的原子的电负性及其共价半径.诱导效应指     

氯化烷基眯唑系列离子液体标准摩尔燃烧焓和生成焓

用精密氧弹热量计测定了4种离子液体：氯化1-甲基-3-乙基咪唑（C2MIC）,氯化1-甲基-3-丁基咪唑（c4MIC）,氯化1-甲基-3-戊基咪唑（C5MIC）和氯化1-甲基-3-己基咪唑（C6MIC）的燃烧热,计算了它们的标准摩尔燃烧焓△cHm^ 和标准摩尔生成焓△fHm^ ,结合文献中的标准摩尔溶解焓,估算了烷基咪唑阳离子在水溶液中的标准摩尔生成焓,以及亚甲基对标准摩尔燃烧焓和标准摩尔生成焓的贡献．     

化学反应焓的图解分析

化学反应焓是物理化学学习的重点和难点,通过教学实践发现,设计生成焓与反应焓关系、 燃烧焓与反应焓关系的能级图,能够简化计算过程,而且可以清楚得区别反应焓、生成焓和燃烧焓。     

过渡元素卤化物标准生成焓的连接性拓扑研究

基于邻接矩阵和成键原子的价环值（Ｖ１）,建立２个新连接性指数（＾０Ｈ,＾１Ｈ）。它们与３３种过渡元素卤化物标准生成焓的直线方程为：－△Θｍ＝－３８．３９＋２２８．０８＾０Ｈ,ｒ＝０．９９０３－△ｆＨΘｍ＝１２７．４５＋３１８．５０＾１Ｈ,ｒ＝０．９８４０与其它指数相比,新指数计算更为准确。结果表明,＾０Ｈ、＾１Ｈ具有良好的结构选择性和性质相关性,可用于预测其它过渡元素卤化物的标准生成焓。     

诱导效应指数与含硫含氮的低碳直链有机化合物的标准汽化热

本文利用诱导效应指数建立了含硫含氮的低碳直链有机物的标准汽化热的简单估算方法，我们利用此法计算了一些含硫含氮的直链有机物的标准汽化热，４１个可比较值的相对误差均在５％以内。     

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.     

Estimation des enthalpies de vaporisation des composes organiques liquides. Partie 1. Applications aux alcanes,cycloalcanes, alcenes,hydrocarbures benzeniques,alcools, alcanes thiols,chloro et bromoalcanes,nitriles, esters,acides et aldehydes

Development of the method used by Benson's group for estimating enthalpies of vaporization permits calculation of the enthalpies of formation of the following classes of organic compound in the liquid phase: alkanes, cycloalkanes, alkenes, chloro- and bromoalkanes, alcohols, acids, aldehydes, esters, nitriles, aromatic hydrocarbons, and mercaptans. For high polarity molecules, some correction terms must be introduced into the calculation.     

An improved empirical force field for saturated hydrocarbons

A new molecular mechanics force field for alkanes is presented. The force field aims to eliminate some identified failures of the well-known MM2 force field. The new energy function gives an improved prediction of the rotational barriers of highly congested molecules, a better calculation of short nonbonded contacts, and the correct reproduction of bond elongation in small torsion angles. The calculation of sublimation enthalpies is also improved. The standard deviation of the formation enthalpies for a set of 54 compounds is 0.63 kcal/mol; this compares with the reported value of 0.42 calculated with MM2 and MM3 for different sets. The force field parameters were obtained using a least squares method.     

Theoretical thermochemistry: Enthalpies of formation of a set of nitrogen‐containing compounds

Gas‐phase standard state formation enthalpies of 63 nitrogen‐containing compounds (NCCs) were studied by computational methods. Gaussian‐n and complete basis set composite methods were applied. After the calculation of the set of NCCs, the results were analyzed in several ways. All the seven selected methods depicted various precisions in this work. According to the calculations and further data processing, G4 was proven to be appropriate and capable of formation enthalpy calculations on NCCs with a mean absolute deviation of 0.63 kcal/mol. Thus, G4 calculation may help us on choosing experimental values and conducting predictions. Isodesmic reactions using G4 methods are also conducted and further correction was given. The high accuracy of G4 method makes it reliable for calculating gas‐phase enthalpies of formations and allows them to serve as a valuable check on the accuracy of reported experimental data. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Organic carbonates: experiment and ab initio calculations for prediction of thermochemical properties

This work has been undertaken in order to obtain data on thermodynamic properties of organic carbonates and to revise the group-additivity values necessary for predicting their standard enthalpies of formation and enthalpies of vaporization. The standard molar enthalpies of formation of dibenzyl carbonate, tert-butyl phenyl carbonate, and diphenyl carbonate were measured using combustion calorimetry. Molar enthalpies of vaporization of these compounds were obtained from the temperature dependence of the vapor pressure measured by the transpiration method. Molar enthalpy of sublimation of diphenyl carbonate was measured in the same way. Ab initio calculations of molar enthalpies of formation of organic carbonates have been performed using the G3MP2 method, and results are in excellent agreement with the available experiment. Then the group-contribution method has been developed to predict values of the enthalpies of formation and enthalpies of vaporization of organic carbonates.     

Calculation of the Vapour Pressure of Organic Molecules by Means of a Group-Additivity Method and Their Resultant Gibbs Free Energy and Entropy of Vaporization at 298.15 K

The calculation of the vapour pressure of organic molecules at 298.15 K is presented using a commonly applicable computer algorithm based on the group-additivity method. The basic principle of this method rests on the complete breakdown of the molecules into their constituting atoms, further characterized by their immediate neighbour atoms. The group contributions are calculated by means of a fast Gauss–Seidel fitting algorithm using the experimental data of 2036 molecules from literature. A ten-fold cross-validation procedure has been carried out to test the applicability of this method, which confirmed excellent quality for the prediction of the vapour pressure, expressed in log(pa), with a cross-validated correlation coefficient Q² of 0.9938 and a standard deviation σ of 0.26. Based on these data, the molecules’ standard Gibbs free energy ΔG°_vap has been calculated. Furthermore, using their enthalpies of vaporization, predicted by an analogous group-additivity approach published earlier, the standard entropy of vaporization ΔS°_vap has been determined and compared with experimental data of 1129 molecules, exhibiting excellent conformance with a correlation coefficient R² of 0.9598, a standard error σ of 8.14 J/mol/K and a medium absolute deviation of 4.68%.