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71.
Jeffrey Axten Jennifer Troy Peter Jiang Mendel Trachtman Charles W. Bock 《Structural chemistry》1994,5(2):99-108
Ab initio molecular orbital calculations are used to study the modified Schlenk equilibrium: 2RMgCl (RMgCl)2 MgR2 + MgCl2 Mg(Cl2)MgR2 with R=H and CH3. In the absence of any solvents, calculations indicate that the formation of the various possible bridged dimers (RMgCl)2 is substantially exothermic. However, using dimethylether as a model solvent, we show that the formation of the dimer (Me2O)(CH3)Mg(Cl2)Mg(CH3)(OMe2) is exothermic only when entropic effects are included. 相似文献
72.
Ahmad Rouhollahi Mohammad Kazem Amini Mojtaba Shamsipur 《Journal of solution chemistry》1994,23(1):63-74
Proton NMR was used to study the complexation reaction between lead ion and 18-crown-6 in a number of binary acetonitrile-water mixtures. Formation constant for the resulting 11 complexes in different solvent mixtures was determined by computer fitting of the chemical shift-mole ratio data. There is an inverse relationship between the complex stability and amount of water in the mixed solvent. The dissociative kinetics of the complex was studied by proton line-shape analysis. The Arrhenius plots showed a distinct isokinetic temperature at about 25°C at which the decomplexation rate is more or less independent of the solvent composition. the complexation rate and the activation parameters E
a
, H and S, for the exchange have been determined and found to be strongly solvent dependent. There is actually a linear relationship between the mole fraction of acetonitrile in the mixed solvent and logarithm of the stability constant as well as activation parameters. 相似文献
73.
The results of kinetic studies on ligand substitution in [M3(CO)11X]– complexes (M = Ru, Os; X = Cl, Br, I) are summarized. The [Os3(CO)11X]– complexes react with PPh3 under mild conditions to initially yield monosubstituted products [Os3(CO)10(PPh3)X]–. The rate of CO substitution obeys a first-order equation with respect to the concentration of the complex and does not depend on the ligand concentration. The rates of the reactions decrease in the order Cl > Br > I withH values increasing from 15 to 18 kcal mol–1 and S
values varying from –19 to –13 cal mol–1 K–1. The enhanced reactivities of these complexes as well as the low activation energies and negative activation entropies are discussed in terms of the effects of -X bridge formation on the transition state of the reaction. Reactions of PPN[Ru3(CO)11–x
(Cl)] (PPN is the bis(triphenylphosphine)iminium cation;x=0, 1) and PPN[Ru3(CO)9(3-I)] with alkynes are also reported. The reactivities of alkynes follow the order BuCCH PhCCH EtCCEt PhCCPh. The higher rates of the reactions of monosubstituted acetylenes compared with those of their disubstituted analogs are explained by agostic interaction between the metal atom and the C-H bond in the reaction transition state and by steric effects. The results obtained attest that the reaction with alkynes occursvia intermediates containing halide bridges and that 3-halide complexes are more reactive than 2-halide complexes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1540–1545, September, 1994.This work was supported by a Presidential Grant from Northwestern University. One of the authors (F. Basolo) wishes to thank Academician M. E. Vol'pin for the invitation to participate in the Workshop The Modern Problems of Organometallic Chemistry (INEOS-94) and Academician O. M. Nefedov for the invitation to publish a review in theRussian Chemical Bulletin. 相似文献
74.
75.
A. K. Galwey 《Journal of Thermal Analysis and Calorimetry》2005,82(2):423-437
Summary A representational model, proposed to account for the physical changes that accompany the melting of alkali halides, was described
in Part 1 [1]. The liquid is portrayed as undergoing continual dynamic structural reorganization of its constituent ions between
individual small domains, zones of various regular, crystal-type arrays. These alternative arrangements are stabilized by
the enthalpy of melting, which, in liquids, relaxes the restriction for solids that only the single, most stable, crystal
structure can be present. The dynamic character of the melt accounts for its fluid character and the loss of long-range order
[1, 2]. This model is extended here to consider the phase diagrams of binary, common ion, alkali halide mixtures comprehensively
reviewed in [3]. Factors determining whether each of these yields a eutectic, or a solid solution, on cooling are discussed
and several trends in the 70-phase diagrams are identified. Eutectic formation, involving maintenance of the liquid state
below the melting points of the pure components, is ascribed to the participation, in an extended dynamic equilibrium, of
additional domains having the regular structures characteristic of double salts. The known crystalline double binary halides
[3], Li/Cs or Rb/F, Cl, Br or I, melt at temperatures well below those of the simpler pure component salts. It is concluded
that the set/liq model for melting, proposed in [1, 2], accounts for some important properties of the phase diagrams presented
in [3]. 相似文献
76.
银微电极微分电位溶出分析法研究 总被引:3,自引:1,他引:3
本文首次报道了银微电极微分电位溶出分析法。用化学刻蚀法方便地制作了银微电极,用于DPSA具有背景值低,分辨率好、精密度及灵敏度高,在不搅拌,仅需一定酸度而酸度而无其它介质的条件下就能测试等优点,对人工试样及自来水样分析,结果令人满意。 相似文献
77.
78.
79.
CHENG Li-Chuan LI Hao-Hong CHEN Zhi-Rong LI Jun-Qian HUANG Chang-Cang CAI Zeng-Liang 《结构化学》2007,26(11)
A new lead(Ⅱ) iodide coordination polymer [(npq)(PbI3)]n 1 (npq = N-propyl- quinolinium) has been synthesized in the presence of npq as structure-directing reagent (SDA). Compound 1 crystallizes in the orthorhombic system, space group Pbca, with a = 19.158(4), b = 7.9909(16), c = 22.929(5) (A), V = 3510.2(12) (A)3, Z = 8, Dc = 2.877 g/cm3, F(000) = 2672, C12H14I3NPb, Mr = 760.14, μ(MoKα) = 14.872 mm-1, the final R = 0.0431 and wR = 0.1021 for 3678 observed reflections with I>2σ(I). Structure determination indicates that the [PbI3]-n infinite chains in each unit cell shape the sketch of 1, which could be described as the result of face-sharing distorted PbI6 octahedra running along the b axis. Electrostatic interaction between conjugated organic counter-cations and inorganic moieties presents and contributes to the crystal packing. 1 was further characterized with IR and elemental analysis. Based on the crystal structure data, quantum chemical calculation with DFT method was used to reveal the electronic structure and optical property of 1. 相似文献
80.
B. A. Arbuzov Z. G. Isaeva M. G. Belyaeva V. V. Ratner O. N. Kataeva I. A. Litvinov V. A. Naumov 《Russian Chemical Bulletin》1992,41(1):117-119
Oxidation of 2-carene by lead tetraacetate in acetic acid afforded p-menth-1(10),2-dien-7-ol, 2-acetyl-6,6-dimethylbicyclo[3.1.0]hexane, p-menth-2-ene-1,7-diol, p-menth-1-ene-3,7-diol, and 2-(m-tolyl)propanol-2.Deceased.A. M. Butlerov Scientific Research Chemical Institute, V. I. Ul'yanov-Lenin Kazan' State University, 420008 Kazan. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 147–150, January, 1992. 相似文献