二氯苯的蒸发焓和升华焓测定

在进行分子内非键合相互作用的热化学研究中,我们已用燃烧量热法测定了各种取代的氯代苯在凝聚态的标准生成焓。为了排除分子间的相互作用,以得到准确的气态生成焓,需要这些化合物的标准蒸发焓或升华焓。文献中这类数据不多,且相当一部分是用测量蒸气压随温度变化按Clapeyron-Clausius方程计算的,不如直接量热法准确。对高取代的氯代苯,由于蒸气压很低,实验困难,数据更缺。为此,我们用量热法测定了三个二氯苯异构体的蒸发焓和升华焓,并结合已有的文献数据,建立了氯代苯标准蒸发焓和升华焓与其沸点的线性关系,估算了其余未知的数据。     

肌醇在氯化钠水溶液中的稀释焓和焓对相互作用

应用微量热法测定了298.15K时肌醇在纯水和氯化钠水溶液中的稀释焓,根据McMillan-Mayer理论计算了肌醇在不同浓度的氯化钠溶液中的2到4阶焓相互作用系数.结果表明,肌醇在氯化钠溶液中的焓对相互作用系数h2均为负值,并且随着氯化钠浓度的增大,h2的值呈增大趋势.根据溶质-溶质相互作用和溶质-溶剂相互作用对焓对相互作用系数的变化趋势进行了解释.     

石油馏分恒压比热容与焓的研究

用差示扫描量热计（ＤＳＣ）测定５个国产原油馏分在系列温度下的恒压比热容，给出比热容与温度的关联式。经标准物质α－Ａｌ２Ｏ３和正庚烷的恒压比热容测定表明，与文献数据的平均偏差在±２％以内。由恒压比热容计算馏分相应温度下的焓，与落入式铜量热计直接量热所得的结果比较，符合良好。还考察８个恒压比热容计算方法的这些馏分的适用性。     

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。     

二氯丁烷标准蒸发焓的测定

用直接量热法测量了五种二氯丁烷位置异构体的标准蒸发焓值,探讨了二氯代烷烃液态蒸发焓的影响规律.     

对二甲氧基苯的标准生成焓

本文报道了用精密转动弹量热计测定对二甲氧基苯的燃烧热和升华热并由此计算出固态和气态下对二甲氧基苯的标准生成焓.结果表明数据的测不准性为平均值总标准偏差的二倍.     

等温稀释型量热计的建立和过量焓的测定

本文建立了一套等温稀释型量热计, 该量热计可用于吸热型体系过量焓的测定,量热计灵敏度为2μV.J^-^1, 恒温精度为±8*10^-^3K。经环己烷-苯体系和环己烷-正己烷体系在298.15K时标定, 精确度在15%以内, 测定了缔合体系在乙醇 -苯体系303.15K时溶液的过量焓。     

木糖醇在纯水和碱金属卤化物水溶液中的稀释焓

应用等温流动微量热法测定了298.15 K时木糖醇在纯水和碱金属卤化物水溶液中的稀释焓, 根据McMillan- Mayer理论计算了木糖醇在溶液中的二到四阶焓相互作用系数. 结果表明, 木糖醇在碱金属卤盐溶液中的焓对相互作用系数h₂均为正值, h₂值随着碱金属阳离子或卤素阴离子半径的增大皆依次增大. 根据木糖醇参与的溶质-溶质, 溶质-溶剂等弱相互作用, 对该种多元醇在碱金属卤盐水溶液中的焓相互作用系数的变化进行了解释.     

三种氨基酸从水到DMSO水溶液的迁移焓研究

用微量量热法测定甘氨酸、L-丙氨酸、L-丝氨酸在二甲基亚砜(DMSO)水溶液中的溶解焓, 计算得到三种氨基酸从水到DMSO水溶液的迁移焓, 根据共球交盖模型对氨基酸与DMSO在水溶液中的相互作用进行讨论, 并与前期的氨基酸在尿素水溶液体系中的迁移焓进行比较. 结果显示, 氨基酸与共溶剂分子之间产生的静电相互作用以及亲水-亲水相互作用对氨基酸迁移焓有负贡献, 而亲水-疏水、疏水-疏水相互作用对氨基酸迁移焓有正贡献. 与尿素水溶液中氨基酸迁移焓的绝对值随尿素浓度的增加而增加, 并规律性地出现多个变化点的情况不同, 氨基酸从水到DMSO水溶液的迁移焓随DMSO浓度的增加而线性增加. 这种差异反映了尿素与DMSO及其水溶液结构的不同, 为认识尿素在水溶液中的缔合作用提供了对比依据.     

mezo-和d, l-2, 3-二氯丁烷气态生成焓的测定

本文用直接量热法测量了298.15K时meso-和d, l-2, 3-二氯丁烷的液态蒸发焓值以及其混合物的液态燃烧焓值, 得到了它们的标准气态生成焓值, 考察了二氯烷烃分子内氯原子间的相互影响和相互作用对其气态生成焓值的影响。     

Energetics of C-F, C-Cl, C-Br, and C-I bonds in 2-haloethanols. enthalpies of formation of XCH(2)CH(2)OH (X = F, Cl, Br, I) compounds and of the 2-hydroxyethyl radical

The energetics of the C-F, C-Cl, C-Br, and C-I bonds in 2-haloethanols was investigated by using a combination of experimental and theoretical methods. The standard molar enthalpies of formation of 2-chloro-, 2-bromo-, and 2-iodoethanol, at 298.15 K, were determined as Delta(f)H(degree)m(CH2CH2OH, l) = -315.5 +/- 0.7 kJ.mol-1, Delta(f)H(degree)mBrCH2CH2OH, l) = -275.8 +/- 0.6 kJ.mol-1, Delta(f)H(degree)m(ICH2CH2OH, l) = -207.3 +/- 0.7 kJ.mol-1, by rotating-bomb combustion calorimetry. The corresponding standard molar enthalpies of vaporization, Delta(vap)H(degree)m(ClCH2CH2OH) = 48.32 +/- 0.37 kJ.mol-1, Delta(vap)H(degree)m(BrCH2CH2OH) = 54.08 +/- 0.40 kJ.mol-1, and Delta(vap)H(degree)m(ICH2CH2OH) = 57.03 +/- 0.20 kJ.mol-1 were also obtained by Calvet-drop microcalorimetry. The condensed phase and vaporization enthalpy data lead to Delta(f)H(degree)m(ClCH2CH2OH, g) = -267.2 +/- 0.8 kJ.mol-1, Delta(f)H(degree)m(BrCH2CH2OH, g) = -221.7 +/- 0.7 kJ.mol-1, and Delta(f)H(degree)m(ICH2CH2OH, g) = -150.3 +/- 0.7 kJ.mol-1. These values, together with the enthalpy of selected isodesmic and isogyric gas-phase reactions predicted by density functional theory (B3LYP/cc-pVTZ) and CBS-QB3 calculations were used to derive the enthalpies of formation of gaseous 2-fluoroethanol, Delta(f)H(degree)m(FCH2CH2OH, g) = -423.6 +/- 5.0 kJ.mol-1, and of the 2-hydroxyethyl radical, Delta(f)H(degree)m(CH2CH2OH, g) = -28.7 +/- 8.0 kJ.mol-1. The obtained thermochemical data led to the following carbon-halogen bond dissociation enthalpies: DHo(X-CH2CH2OH) = 474.4 +/- 9.4 kJ.mol-1 (X = F), 359.9 +/- 8.0 kJ.mol-1 (X = Cl), 305.0 +/- 8.0 kJ.mol-1 (X = Br), 228.7 +/- 8.1 kJ.mol-1 (X = I). These values were compared with the corresponding C-X bond dissociation enthalpies in XCH2COOH, XCH3, XC2H5, XCH=CH2, and XC6H5. In view of this comparison the computational methods mentioned above were also used to obtain Delta(f)H(degree)m-594.0 +/- 5.0 kJ.mol-1 from which DHo(F-CH2COOH) = 435.4 +/- 5.4 kJ.mol-1. The order DHo(C-F) > DHo(C-Cl) > DHo(C-Br) > DHo(C-I) is observed for the haloalcohols and all other RX compounds. It is finally concluded that the major qualitative trends exhibited by the C-X bond dissociation enthalpies for the series of compounds studied in this work can be predicted by Pauling's electrostatic-covalent model.     

Metal fluorides form strong hydrogen bonds and halogen bonds: measuring interaction enthalpies and entropies in solution

The organometallic compound trans-(tetrafluoropyrid-2-yl)bis(triethylphosphine)-fluoronickel(II) (NiF) is shown to serve as a strong hydrogen bond and halogen bond acceptor in solution via intermolecular interactions with the fluoride ligand. The nature of the interactions has been confirmed by multinuclear NMR spectroscopy. Experimental binding constants, enthalpies, and entropies of interaction with hydrogen-bond-donor indole and halogen-bond-donor iodopentafluorobenzene have been determined by 19F NMR titration. In toluene-d8 solution indole forms a 1:1 and 2:1 complex with NiF (K1 = 57.9(3), K2 = 0.58(4)). Interaction enthalpies and entropies are -23.4(2) kJ mol-1 and -44.5(8) J mol-1 K-1, respectively, for the 1:1 complex; -14.8(8) kJ mol-1 and -53(3) J mol-1 K-1, respectively, for the 2:1 complex. In toluene-d8 solution iodopentafluorobenzene forms only a 1:1 complex (K1 = 3.41(9)) with enthalpy and entropy of interaction of -16(1) kJ mol-1 and -42(4) J mol-1 K-1, respectively. A marked solvent effect was observed for the halogen bond interaction. NMR titrations in heptane solution indicated formation of both 1:1 and 2:1 complexes of iodopentafluorobenzene with NiF (K1 = 21.8(2), K2 = 0.22(4)). Interaction enthalpies and entropies are -26(1) kJ mol-1 and -63(4) J mol-1 K-1, respectively, for the 1:1 complex; -21(1) kJ mol-1 and -83(5) J mol-1 K-1, respectively, for the 2:1 complex. There is a paucity of such experimental energetic data particularly for halogen bonds despite substantial structural data. These measurements demonstrate that halogen bonds are competitive with hydrogen bonds as intermolecular interactions and provide a suitable benchmark for theoretical calculations and quantitative input into design efforts in supramolecular chemistry and crystal engineering.     

C-H bond dissociation enthalpies in norbornane. An experimental and computational study

Gas-phase C-H bond dissociation enthalpies (BDEs) in norbornane were determined by quantum chemistry calculations and the C2-H BDE was experimentally obtained for the first time by time-resolved photoacoustic calorimetry. CBS-Q and CBS-QB3 methods were used to derive the values DH degrees (C1-H) = 449 kJ mol-1, DH degrees (C7-H) = 439 kJ mol-1, and DH degrees (C2-H) = 413 kJ mol-1. The experimental result DH degrees (C2-H) = 414.6 +/- 5.4 kJ mol-1 is in excellent agreement with the theoretical value. The trend DH degrees (C1-H) > DH degrees (C7-H) > DH degrees (C2-H) is discussed.     

卟啉化合物的热化学研究: V. 含溴卟啉化合物的标准燃烧能和生成焓

用本实验室建立的精密转动氧弹燃烧热量计测定了标准物质对溴苯甲酸、辅助物质鲨烷及四对溴苯基卟啉(Tp-BrPP)的标准燃烧能, 并计算出了它们的标准生成焓。     

Thermochemical studies on 3-methyl-quinoxaline-2-carboxamide-1,4-dioxide derivatives: enthalpies of formation and of N-O bond dissociation

The standard molar enthalpies of formation of the 3-methyl-N-R-2-quinoxalinecarboxamide-1,4-dioxides (R = H, phenyl, 2-tolyl) in the gas phase were derived using the values for the enthalpies of combustion of the crystalline compounds, measured by static bomb combustion calorimetry, and for the enthalpies of sublimation, measured by Knudsen effusion, at T = 298.15 K. These values have also been used to calibrate a computational procedure that has been employed to estimate the gas-phase enthalpies of formation of the corresponding 3-methyl-N-R-2-quinoxalinecarboxamides and also to compute the first, second, and mean N-O bond dissociation enthalpies in the gas phase. It is found that the size of the substituent almost does not influence the computed N-O bond dissociation enthalpies; the maximum enthalpic difference is approximately 5 kJ.mol-1.     

Thermochemistry of methyl and ethyl nitro, RNO2, and nitrite, RONO, organic compounds

Computational quantum theory is employed to determine the thermochemical properties of n-alkyl nitro and nitrite compounds: methyl and ethyl nitrites, CH3ONO and C2H5ONO, plus nitromethane and nitroethane, CH3NO2 and C2H5NO2, at 298.15 K using multilevel G3, CBS-QB3, and CBS-APNO composite methods employing both atomization and isodesmic reaction analysis. Structures and enthalpies of the corresponding aci-tautomers are also determined. The enthalpies of formation for the most stable conformers of methyl and ethyl nitrites at 298 K are determined to be -15.64 +/- 0.10 kcal mol-1 (-65.44 +/- 0.42 kJ mol-1) and -23.58 +/- 0.12 kcal mol-1 (-98.32 +/- 0.58 kJ mol-1), respectively. DeltafHo(298 K) of nitroalkanes are correspondingly evaluated at -17.67 +/- 0.27 kcal mol-1 (-74.1 +/- 1.12 kJ mol-1) and -25.06 +/- 0.07 kcal mol-1 (-121.2 +/- 0.29 kJ mol-1) for CH3NO2 and C2H5NO2. Enthalpies of formation for the aci-tautomers are calculated as -3.45 +/- 0.44 kcal mol-1 (-14.43 +/- 0.11 kJ mol-1) for aci-nitromethane and -14.25 +/- 0.44 kcal mol-1 (-59.95 +/- 1.84 kJ mol-1) for the aci-nitroethane isomers, respectively. Data are evaluated against experimental and computational values in the literature with recommendations. A set of thermal correction parameters to atomic (H, C, N, O) enthalpies at 0 K is developed, to enable a direct calculation of species enthalpy of formation at 298.15 K, using atomization reaction and computation outputs.     

Combined experimental and computational study of the thermochemistry of the fluoroaniline isomers

The standard (p degrees = 0.1 MPa) molar enthalpies of formation in the condensed phase of all the fluoroanilines, with the exception of the 2,3,5-trifluoroaniline compound, were derived from the standard molar energies of combustion in oxygen at T = 298.15 K, measured by rotating bomb combustion calorimetry. Calvet high-temperature vacuum sublimation experiments were performed to measure their enthalpies of vaporization or sublimation. These experiments allowed the determination of the standard molar enthalpies of formation in the gaseous phase and at T = 298.15 K. These values are also compared with estimates based on G3MP2B3 and BP86/6-31+G(d) computations, which have been extended also to the fluoroaniline that was not studied experimentally. The results are in close agreement with a mean deviation of approximately 3 kJ.mol-1. The largest difference between experimental and G3MP2B3 values is found for the pentafluoroaniline (-7.0 kJ.mol-1). For the three monofluoroanilines, the composite approach has been used also to compute gas-phase acidities, electron and proton affinities, ionization enthalpies and N-H bond dissociation enthalpies. The computed values compare well with available experimental results supporting the new computed data.     

5-氨基间苯二甲酸钠和5-羟基间苯二甲酸钠的热力学性质

在水溶液中合成了5-氨基间苯二甲酸钠(1)和5-羟基间苯二甲酸钠(2)固态样品,元素分析和TG-DTG确定其组成符合C8H5O4NNa2·H2O(1)和C8H4O5Na2·H2O(2).用精密自动绝热热量计测定了它们在78～400K温区的低温热容,将实验值用最小二乘法拟合,得到热容随温度变化的多项式方程,用此方程进行数值积分,得到该温区内每隔5K的舒平热容值和各种热力学函数值.用RD496-2000型微热量计测定了样品在298.15K时的标准摩尔溶解焓分别为ΔsolHmθ(1,s)=-44.552±0.164kJmol-1和θΔsolHm(2,s)=-36.055±0.154kJmol-1,计算了其水合阴离子标准摩尔生成焓分别为θΔfHm(C8H5O4N2-,aq)=-684.56±1.67kJmol-1和ΔfHmθ(C8H4O52-,aq)=-1263.43±2.13kJmol-1.用RBC-II型精密转动弹热量计测定了样品的恒容燃烧热分别为ΔcU(1,s)=-13382.14±5.28Jg-1和ΔcU(2,s)=-10339.15±4.15Jg-1,计算了它们的标准摩尔燃烧焓和标准摩尔生成焓分别为ΔcHmθ(1,s)=-3252.90±1.28kJmol-1和θΔcHm(2,s)=-2522.64±1.01kJmol-1,ΔfHmθ(1,s)=-1406.46±1.66kJmol-1,θΔfHm(2,s)=-1993.79±1.46kJmol-1.     

Thermochemistry of aromatic ketones. Experimental enthalpies of formation and structural effects

The standard enthalpies of formation Δ_fH^o (liq. or cr.) at the temperature T = 298.15 K were measured using combustion calorimetry for benzophenone (A), 1-indanone (B), -tetralone (C), 9-fluorenone (D), anthrone (E) and dibenzosuberone (F). The standard enthalpies of vaporization Δ_vH^o or sublimation Δ_sH^o of A-F and 5,7-dihydro-6H-dibenzo[a,c]cyclohepten-6-one (G) were obtained from the temperature function of the vapor pressure measured in a flow system. Enthalpies of fusion Δ_mH of solid compounds were measured by DSC. From the enthalpies of formation of the gaseous compounds of A-G the values of their strain enthalpies were derived and structural effects discussed.