Thermodynamic parameters for the reaction of 1,8-diazabicyclo [5.4.0] undec-7-ene with 4-nitrophenylnitromethane in several aprotic solvents

Equilibrium constants K for reaction of the C-acid, 4-nitro/phenylnitromethane with 1,8-diazabicyclo [5.4.0] undec-7-ene have been determined in aprotic solvents over a range of temperature. Corresponding measurements have been made for the deuterated acid 4-NPNM-d₂. Thermodynamic parameters K, H^o and S^o, for proton and for deuteron transfers are not very differet in a given solvent, but show a considerable solvent dependence. There is an increase in magnitude of K with increase in solvent dielectric constant, a finding which is consistent with formation of an ion-pair. The range of extent of exothermicity of the reaction is quite small, –40 to-65 kJ-mol^–1, and the values of S^o (large, negative) indicate, in general, increasing solvent restriction by the product with increasing solvent polarity. A modest bathochromic solvatochromism of the product is observed as the dielectric constant increases.     

Hybrid integral-equation/simulation models: from complexation thermodynamics to direct free energies.

Statistical-mechanical integral equation theory, an approximate methodology for computing distribution functions and thermodynamic properties of the liquid state, can be advantageously combined with molecular simulations to overcome inherent limitations of both approaches. This Concept discusses a number of conceptual applications that illustrate the capabilities of hybrid models: A study of complex formation in solution by explicit simulation of only the solute molecules, the correction of artefacts induced by truncated potentials, and an approach to the direct computation of free energies from a simulation of a single state.     

Potentiometric study of the acid-base equilibrium of loprazolam at 25 °C in 0.1M NaCl medium

The acid-base behaviour of Loprazolam has been studied using an automated potentiometric titration system. The temperature was kept constant at 25 °C and the ionic medium was 0.1 mol dm^–3 NaCl in different ethanol-water mixtures (5–20%). The values of the constants obtained at the different ethanol compositions have been extrapolated to give the corresponding stoichiometric constant in water, log = 6.39 ± 0.15     

PBMA-b-PSt磺化嵌段离聚体在DMF溶液中的聚集行为

采用激基缔合物荧光光谱法研究了轻度磺化聚甲基丙烯酸丁酯－b－聚苯乙烯（PBMA-b－PSt）嵌段离聚体在极性溶剂N，N－二甲基甲酰胺（DMF）溶液中的聚集行为；发现嵌段离聚体的磺化度和浓度强烈影响溶液中聚合物链的聚集态结构，不同的磺化度样品具有不同的临界聚集浓度；随磺化度增加，聚合物链缠绕密集，形成具有多苯环的聚集体，而且当磺化度为摩尔分数x＝3．59％时，荧光发射光谱最大发射峰波长出现最大红移，临界聚集浓度最低，说明最容易形成多苯环聚集体，该磺化点可以认为是磺化聚甲基丙烯酸丁酯－b－聚苯乙烯体现离聚体行为和聚电解质行为的临界磺化度。     

The effect of cation size on ion pairing of methyl orange dye with tetraalkylammonium and benzyltrialkylammonium ions in aqueous solution

Formation constants have been measured by a solvent distribution method for the ion pairing of an arene sulfonate, methyl orange dye, with two series of quaternary ammonium ions: R₄N⁺(R=Et,n-Pr,n-Bu, andn-Pent) and C₆H₅CH₂R₃N⁺ (R=Me, Et,n-Pr,n-Bu,n-Pent, andn-Hex). Ion pairing increases dramatically as the length of the R group increases beyond butyl. Using a hard-sphere model for contact ion pairs, it is estimated that coulombic attraction contributes about –kT to the binding free energy and decreases slightly with increasing size of R₄N⁺. Other factors related to solvation effects, of which cosphere overlap predominates, contribute from –2kT to –7kT of binding energy. Plots of logK for association as a function of cation size show an inflection with decreasing slope between R=propyl and R=butyl. Possible causes for the inflection are considered.     

溶剂红135染料中六氯苯含量的测定

溶剂染料是高级塑料着色剂及聚酯纺前着色剂,具有着色力强、耐热性好、耐晒牢度高,色泽鲜艳等优点,在日用塑料、有机玻璃、PVC包装材料、装饰材料、油漆油墨、色母粒等材料的着色,化纤、涤纶、尼龙、醋酸纤维等着色喷丝上应用广泛。溶剂染料属油溶性染料范畴,能溶解于有机溶剂,     

降冰片二烯衍生物光敏异构化反应的机理研究

利用甲基卡唑为光敏剂，实现了三个降冰片二烯衍生物的光诱导介键异构化反应，荧光猝灭，化学诱导动态核极化（ＣＩＤＮＰ）以及热力学讨论都支持电子转移敏化机理，有关量子效率的计算表明单重态电子转移机制对光异构化反应的贡献远大于三重态能传递机制，此外还探讨了光异构化反应中的溶剂极性效应。     

Conductance study of the thermodynamics of some transition and heavy metal cryptates in binary acetonitrile-dimethylsulfoxide mixtures

A conductance study of the interaction between Co²⁺, Ni²⁺, Cu²⁺, Cd²⁺, Zn²⁺ and Pb²⁺ ions with cryptands C211, C221 and C222 in different acetonitrile-dimethylsulfoxide mixtures has been carried out at various temperatures. The formation constants of the resulting metal cryptates were determined from the molar conductance-mole ratio data. It was found that the stability of Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺ cryptates vary in the order C211>C221>C222, while for Cd²⁺ cryptates the stability order is C221>C222>C211. A linear relationship is observed between logK _f of different metal cryptates and the mole fraction of acetonitrile in the solvent mixture. The enthalpy and entropy of cryptate formation reactions were determined from the temperature dependence of the formation constants. The enthalpy and entropy changes are quite sensitive to the solvent composition and the resultingTS ⁰–H ⁰ plot shows a fairly good linear correlation, indicating the existence of an entropy-enthalpy compensation in the cryptate formation reactions. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82181 (30 pages).     

溶剂种类及组成对纤维素羧甲基化反应的影响

溶剂种类及组成对纤维素羧甲基化反应的影响张镜吾，程发，李东立，李桂风，张晓红（天津大学化学系，天津，３０００７２）关键词纤维素，混合溶剂，碱处理，羧甲基化．Ｘ－衍射校甲基纤维素（ＣＭＣ）是重要的纤维素衍生物，应用领域十分广泛．纤维素核甲基化反应主要取...