Thermal [1,5] sigmatropic rearrangements in (σ-7-cycloheptatrienyl)triphenyltin and (σ-5-cyclohepta-1,3-dienyl)triphenyltin: A 1H and 13C NMR reinvestigation

It has been confirmed by ¹H and ¹³C NMR spectroscopies that Sn(σ-C₇H₇)Ph₃ undergoes either 1,4- or 1,5-shifts of the SnPh₃ moiety around the cycloheptatrienyl ring with ΔH³ = 13.8 ± 0.4 kcal mol^?1, ΔS3 = ?5.6 ± 1.2 cal mol^?1 deg^?1, and ΔG³₃₀₀ = 15.44 ± 0.14 kcal mol^?1. Similarly, (σ-5-cyclohepta-1,3-dienyl)triphenyltin undergoes 1,5-shifts with ΔH³ = 12.4 ± 0.6 kcal mol^?1, ΔS³ = ?11.2 ± 1.8 cal mol^?1 deg^?1, and ΔG³₃₀₀ = 15.76 ± 0.13 kcal mol^?1. It is therefore probable that Sn(σ-5-C₅H₅)R₃ and Sn(σ-3-indenyl)R₃ do not undergo 1,2-shifts as previously suggested but really undergo 1,5-shifts.     

Addition of ethyl radicals to carbon monoxide. Kinetic and thermochemical properties of the propionyl radical

Azoethane was irradiated in the presence of carbon monoxide in the temperature range of 238 to 378 K. Kinetic parameters for the addition of ethyl radicals to carbon monoxide and for the decomposition of propionyl radicals were determined. The rate constants were found to be log k(cm³ mol^?1 sec^?1) = 11.19 - 4.8/θ and log k(sec^?1) = 12.77 - 14.4/θ, respectively. Estimated thermochemical properties of the propionyl radical are ΔH_f⁰ = -10.6 ± 1.0 kcal mol^?1, S⁰ = 77.3 ± 1.0 cal K^?1 mol^?1, and D(C₂H₅CO? H) = 87.4 kcal mol^?1.     

Anionic polymerization of norbornene trisulfide (exo-3,4,5-trithia-tricyclo[5.2.1.02.6]decane)

The anionic polymerization of norbornene trisulfide initiated with sodium thiophenoxide (sodium cation solvated with dibenzo-18-crown-6 ether) was studied. Polymers with high molecular weights were obtained (M _n up to 10⁵, osmometrically). Molecular weights calculated for living polymerization conditions (i.e., one molecule of initiator yields one macromolecule) agree well with M _n measured by osmometry. ¹H-NMR, ¹³C-{¹H}-NMR, and Raman spectra of the polymer are given. Thermodynamics of polymerization in toluene solvent is described. Enthalpy ΔH_ss = ?(1.39 ± 0.17) kcal mol^?1 and entropy ΔS_ss = ?(7.52 ± 0.55) cal mol^?1 deg^?1 coefficients of polymerization were evaluated from the temperature dependence of the equilibrium monomer concentration determined dilatometrically.     

腈菌唑的热容和热力学性质

通过小样品精密自动绝热热量计测定了自己合成并提纯的腈菌唑 (C₁₅H₁₇ClN₄) 在78 ～ 368K温区的低温摩尔热容。量热实验发现, 该化合物在363 ~ 372 K温区, 有一固-液熔化相变过程, 其熔化温度为 (348.800±0.06)K, 摩尔熔化焓、摩尔熔化熵及化合物的纯度分别为：(30931±11) J•mol^-1、(88.47±0.02) J•mol^-1•K^-1和0.9941(摩尔分数)。用差示扫描量热(DSC) 技术对该物质的固-液熔化过程作了进一步研究，结果与绝热量热法一致。     

Low-temperature thermodynamic properties of L- and DL-valines

Heat capacities C _p(T) of L-valine and DL-valine were measured in the temperature range 6–300 K with an adiabatic calorimeter; thermodynamic functions were calculated based on these measurements. At 298.15 K, the values of heat capacity, C _p; entropy, S _m ⁰ (T) ? S _m ⁰ (0); enthalpy, H _m ⁰ (T) ? H _m ⁰ (0) of L-valine are equal, respectively, to 167.9 ± 0.3 J K^?1 mol^?1; 178.5 ± 0.4 J K^?1 mol^?1; and 27510 ± 60 J mol^?1. For DL-valine, these values are equal, respectively, to 167.3 ± 0.3 J K^?1 mol^?1, 174.4 ± 0.3 J K^?1 mol^?1, and 27000 ± 50 J mol^?1. The difference between the heat capacities of enantiomer and racemate has been calculated and compared with the similar data for serines, cysteines, and phenylglycines.     

Kinetic determination of the metalmetal bond dissociation energy in bis(dicarbonyl η5-cyclopentadienyliron)

The ironiron bond energy in [C₅H₅Fe(CO)₂]₂ (I) has been determined by measuring the rate of disproportionation of the monoacetyl complex (AcC₅H₄)(C₅H₅)Fe₂(CO)₄ (II) to I and [AcC₅H₄Fe(CO)₂]₂ (III). The reaction follows first order kinetics in benzene solution in the temperature range of 60–100°C with activation parameters calculated as: ΔH^≠ = 26.9 ± 2.7 kcal mol^?1 and ▽s^≠ = 2.0 ± 3.2 cal mol^?1 deg^?1.     

Low-temperature heat capacity and standard thermodynamic functions of 1-butyl-3-methylimidazolium lactate

The heat capacities of 1-butyl-3-methylimidazolium lactate ionic liquids ([C₄mim][Lact]) were measured with a highly accurate automatic adiabatic calorimeter over the temperature range from 79 to 406 K. And the experimental values of molar heat capacities were fitted to a polynomial equation using least square method in the appropriate temperature ranges. The standard molar heat capacity was determined to be 1734.46?±?5.12 J K^?1 mol^?1 at 298.15 K. The molar enthalpy and molar entropy of the transition were determined to be 15.575?±?0.045 and 64.44?±?0.14 J K^?1 mol^?1. Other thermodynamic properties, such as (H_T???H_298.15) and (S_T???S_298.15), were also calculated. Furthermore, when the temperature reaches 241.87 K, the strongest peaks appeared by analysis of the heat capacity curve. This phenomenon could be explained from the interionic interaction, which is the hydrogen bond between the anions and cations.     

Cesium chromate,Cs2CrO4: heat capacity and thermodynamic properties from 5 to 350 K

The heat capacity of a sample of Cs₂CrO₄ was determined in the temperature range 5 to 350 K by aneroid adiabatic calorimetry. The heat capacity at constant pressure C_p^o(298.15 K), the entropy S^o(298.15 K), the enthalpy {H^o(298.15 K) - H^o(0)} and the function $\text{? {G}{}^{\mathrm{o}}\text{(298.15}\text{K}\text{) - H}{}^{\mathrm{o}}\text{(0)}}\text{298.15}\text{K}$ were found to be (146.06 ± 0.15) J K^?1 mol^?1, (228.59 ± 0.23) J K^?1 mol^?1, (30161 ± 30) J mol^?1, and (127.43 ± 0.13) J K^?1 mol^?1, respectively. The heat capacity C_p^o(298.15 K) and entropy S^o(298.15 K) and entropy S^o(298.15 K) of Rb₂CrO₄ are estimated to be (146.0 ± 1.0) J K^?1 mol^?1 and (217.6 ± 3.0) J K^?1 mol^?1, respectively.     

The tris(picolinate)vanadate(II) ion: Redox properties and electron transfer kinetics with cobalt(III) amines

Vanadium(II) ions form with the pyridine-2-carboxylate ligand a deep blue, tris-substituted complex absorbing at 660 nm (ε = 7.2 × 10³ M^?1) cm^?1) with a shoulder at 450 nm. Reversible spectroelectrochemistry and cyclic voltammetry were observed for this complex, with E_{$\text{1}\text{2}$} = ?0.448 V vs NHE, and ΔS_rc^θ = ?6 cal · mol^?1 · deg^?1. Electron transfer kinetics with [CO(en)₃]³⁺ led to k₁₂ = 3100 M^?1 s^?, ΔH^≠ = 12.4 kcal · mol^?1 and ΔS^≠ = ?0.9 cal · mol^?1 · deg^?1 (I = 0.10 M). For the related [Co(NH₃)₆]³⁺ complex, k₁₃ = 1.9 × 10⁴ M^?1 s^?1. The self-exchange rate constant and activation parameters were analysed in terms of relative Marcus theory.     

Data on the thermochemistry of azoalkanes

The rate constant of the primary decomposition step was determined for four symmetrical and four unsymmetrical azoalkanes. From the experimental activation energies and some literature enthalpy data, the following enthalpies of formation of radicals and group contributions were calculated: ΔH_? (CH₃N₂) = 51.5 ± 1.8 kcal mol^?1, ΔH_? (C₂H₅N₂) = 44.8 ± 2.5 kcal mol^?1, ΔH_? (2?C₃H₇N₂) = 37.9 ± 2.2 kcal mol^?1, [N_A-(C)] = 27.6 ± 3.7 kcal mol^?1, [N_A-(?_A) (C)] = 61.2 ± 3.1 kcal mol^?1.     

4-硝基苯甲醇的低温热容和标准摩尔生成焓

用精密自动绝热量热计测定了4-硝基苯甲醇（4-NBA）在78 ~ 396 K温区的摩尔热容。其熔化温度、摩尔熔化焓及摩尔熔化熵分别为:(336.426 ± 0.088) K, (20.97 ± 0.13) kJ×mol-1 和 (57.24 ± 0.36) J×K-1×mol-1.根据热力学函数关系式,从热容值计算出了该物质在80 ~ 400 K温区的热力学函数值 [HT - H298.15 K] 和[ST - S298.15 K]. 用精密氧弹燃烧量热计测定了该物质在T＝298.15 K的恒容燃烧能和标准摩尔燃烧焓分别为 (C7H7NO3, s)＝- ( 3549.11 ± 1.47 ) kJ×mol-1 和 (C7H7NO3, s)＝- ( 3548.49 ± 1.47 ) kJ×mol-1. 利用标准摩尔燃烧焓和其他辅助热力学数据通过盖斯热化学循环, 计算出了该物质标准摩尔生成焓 (C7H7NO3, s)＝- (206.49 ± 2.52) kJ×mol-1 .     

Kinetic and thermochemical parameters of chlorine atom transfer reactions from CF3Cl,CF3CF2Cl,CF2ClCF2Cl,and CF2ClCFCl2 in gas phase

The following reactions: (1) were studied over the temperature ranges 533–687 K, 563–663 K, and 503–613 K for the forward reactions respectively and over 683–763 K, for the back reaction. Arrhenius parameters for chlorine atom transfer were determined relative to the combination of the attacking radicals. The ΔH_r°(1) = ?3.95 ± 0.45 kcal mol^?1 was calculated and from this value the ΔH∮(C₂F₅Cl) = ?2.66.3 ± 2.5 kcal mol^?1 and D(C₂F₅-Cl) = 82.0 ± 1.2 kcal mol^?1 were obtained. Besides, the ΔH_r°(2) was estimated leading to D(CF₂ClCF₂Cl) = 79.2 ± 5 Kcal mol^?1. The bond dissociation energies and the heat of formation are compared with those of the literature. The effect of the halogen substitutents as well as the importance of the polar effects for halogen transfer processes are discussed.     

KINETICS AND MECHANISTIC ASPECTS OF THE HYDROLYSIS REACTION OF CYCLIC PHOSPHONODITHOITES

Abstract

The hydrolysis of the cyclic phosphonodithioite C₆H₅ P(SCH(CO₂CH₂CH₃CH(CO₂CH₂CH₃)S) in aqueous acetonitrile follows a rate law that is first order in the concentration of C₆H₅ P(SCH(CO₂CH₂CH₃)CH(CO₂CH₂CH₃)S), and independent of the water concentration. The values of E_a , ΔH* and ΔS* are 10.4 k cal mol^?1, 9.6 k cal mol^?1 and -45 cal mol^?1 respectively. The isotope effect for D₂O as compared to H₂O is 2.5. A mechanism is proposed whereby a pre-equilibrium is established between the phosphonodithioite and water, with a subsequent proton transfer from water to the tricoordinate phosphorus occurring in a subsequent step. The slow step involves hydrolytic cleavage of the first phosphorus-sulfur bond. The compound 2-nitro-5-thiocyanatobenzoic acid is used to provide supporting evidence for the formation of an intermediate thiol.     

A kinetic study of the ortho-mercuration of 2-methylazobenzene

The kinetics of the mercuration of 2-methylazobenzene in methanol were studied. The thermodynamic data found were ?E_act = 22.7 kcal mol^?1, ?H¹ = 22.0 kcal mol^?1, and ?S¹ = ?12.3 eu. In comparison with a value of ?S¹ ? ?20 eu for the mercuration of benzene, this lowered entropy is taken as evidence for complex formation between mercuric acetate and 2-methylazobenzene before and during the rate determining step of electrophilic substitution.     

Stereochemical nonrigidity of (O—Ge)-chelate bis[(2-oxo-1-hexahydroazepinyl)methyl]dichlorogermane: substantiation of the dissociative mechanism of chelating ligand exchange

Stereochemical nonrigidity of the hexacoordinated (O—Ge)-chelate bis(2-oxo-1-hexahydroazepinylmethyl)dichlorogermane in CDCl₃ was studied by dynamic NMR. The activation parameters of the intramolecular rearrangement at the coordination center are G ^# ₂₉₈ = 12.3±0.2 kcal mol^–1, H ^# = 16.9±0.2 kcal mol^–1, and S ^# = 15.3±0.7 cal mol^–1 K^–1. The dissociative mechanism of ligand exchange involving the cleavage of the OGe coordination bond is discussed based on the positive entropy of activation.     

Some thermodynamic parameters for hydroxy amino acids: Bicine and tricine

pK values of N,N-dihydroxyethylglycine (bicine) and N-[tris(hydroxymethyl)methyl]-glycine (tricine) have been determined by the Irving-Rossotti method in an aqueous medium at 25, 30, 35, 40, 45, and 50°C and at different ionic strengths (I = 0.1, 0.5, and 1.0). Plots between pK_a(NH) and 1/T for various ionic strengths have been obtained and the values of slopes have been used to calculate the ΔH, ΔS, and ΔG for the dissociation reactions of bicine and tricine. The ΔH, ΔS, and ΔG values for bicine were found to be 10.6 ± 0.6 kcal mol^?1, ?1.9 ± 1.8 e.u., and 11.1 ± 0.06 kcal mol^?1, respectively, and for tricine 11.2 ± 0.6 kcal mol^?1, 1.6 ± 1.6 e.u., and 10.7 ± 0.06 kcal mol^?1, respectively. The pK_a(NH) values decrease with rise in temperature but the influence of ionic strength is not significant.     

The activation energy of the skeletal isomerization in the radical cations of toluene and cycloheptatriene by mass spectrometry of their 2-phenylethyl derivatives

The Unimolecular mass spectrometric fragmentations of the molecular ions of 1,3-diphenylpropane, 1-(7-cycloheptatrienyl)-2-phenylethane and the 1-phenyl-2-tolylethanes and their [d₅]phenyl analogues have been investigated by metastable ion techniques and measurements of ionization and appearance energies. By comparing the formation of [C₇H₇]⁺, [C₇H₈]⁺?, [C₈H₈]⁺? and [C₈H₉]⁺ it is shown that the molecular ions of the four diaryl isomers do not undergo ring expansion reactions of the aromatic nuclei prior to these fragmentations. Conversely, the molecular ions of the cycloheptatrienyl isomer suffer in part a contraction of the 7-membered ring. From these results and from the measured ionization and appearance energies lower limits to the activation energies of these skeletal isomerizations have been estimated yielding E > 33±5 kcal mol^?1 formonoalkylbenzene, E > 20 2±5 kc mol^?1 for 7-alkylcycloheptatriene and E > 40±5 kcal mol^?1 for dialkylvbenzene positive radical ions. Upper limits can be deduced from literature evidence yielding E < 45 kcal mol^?1 for monoalkylbenzene and E < 53 kcal 4mol^?1 for dialkylbenzene positive radical ions. The activation energy thus estimated for monoalkylbenzene is in excellent agreement with the recently calculated value(s) for the toluene ion.     

Kinetics and thermochemistry of the reaction of benzyl radical with O2: Investigations by discharge flow/laser induced fluorescence between 393 and 433 K

The kinetics of the reaction of the benzyl radical with molecular oxygen has been studied between 393 and 433 K. The Discharge Flow technique with detection of benzyl radicals by Laser Induced Fluorescence in their visible absorption band has been used. All experiments have been performed at ≈1 torr in helium as the buffer gas. The radical benzyl decay plots are characteristic of the approach to equilibrium between benzyl and benzylperoxy: benzyl + O₂ $ \mathbin{\lower.3ex\hbox{$\buildrel\textstyle\longrightarrow\over {\smash{\longleftarrow}\vphantom{_{\vbox to.5ex{\vss}}}}$}} $ benzylperoxy (k₃, k_?3). Thanks to a reasonable assumption concerning the standard entropy of the reaction (3) (ΔS₂₉₈°=?29 cal mol^?1 K^?1), based on the additivity rules of Benson, the following reaction enthalpy is derived for reaction (3): ΔH₂₉₈°=(?20 ± 1 kcal mol^?1). This latter value is compared with a few enthalpies of other related reactions available in the literature. © 1993 John Wiley & Sons, Inc.     

Investigation of kinetic and mechanism of triphenylphosphine addition to para‐naphthoquinone

This work reports the results of a kinetic and mechanistic investigations of the addition reaction of triphenylphosphine to para‐naphtoquinone in 1,2‐dichloromethane as solvent. The order of reaction with respect to the reactants was determined using initial rate method, and the rate constant was obtained on the basis of pseudo‐first‐order method. Variable time method using Uv–Vis spectrophotometry (at 400 nm) was utilized for monitoring this addition reaction, for which the following Arrhenius equation was obtained: The resulting activation parameters E_a, ΔH^#, ΔG^#, and ΔS^# at 300 K were 13.63, 14.42, 18.75 kcal mol^?1, and ?14.54 cal mol^?1K^?1, respectively. The results suggest that the reaction is first order with respect to both triphenylphosphine and para‐naphthoquinone. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 427–433, 2005     

Kinetic study of triphenylphosphine addition to para‐benzoquinone

Kinetics of the addition reaction of triphenylphosphine to para‐benzoquinone in 1,2‐dichloroethane as solvent was studied. Initial rate method was used to determine the order of the reaction with respect to the reactants. Pseudo‐first‐order method was also used to calculate the rate constant. This reaction was monitored by UV‐vis spectrophotometry at 520 nm by variable time method. On the basis of the obtained results, the Arrhenius equation of this reaction was obtained: The activation parameters, E_a, ΔH^#, ΔG^#, and ΔS^# at 300 K were 5.701, 6.294, 19.958 kcal mol^?1 and ?45.853 cal mol^?1 K^?1, respectively. This reaction is first and second order with respect to triphenylphosphine and para‐benzoquinone, respectively. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36:472–479, 2004