Michael Addition of Thiols to á,(a)-Unsaturated Carbonyl Compounds Catalyzed by Bifunctional Organocatalysts:Asymmetric Michael Addition and Asymmetric Protonation

Recently the hydrogen-bond activated reactions have attracted much attention.1 Takemoto2 reported a highly enantioselective Michael addition of manolate to nitroolefins catalyzed by a bifunctional organocatalyst with tertiary amine and thiourea moiety. As we known,stereoselective conjugate additions of thiols are interesting due to the standpoint of biological and synthetic importance, however, only very limited good results have been obtained except for the works of Shibasaki3, Kanemasa4 and Deng5 et al.In this letter, we report an efficient catalytic asymmetric Michael reactions of thiols to a,a-unsaturated carbonyl compounds promoted by bifunctional organocatalysts. A series of organocatalysts with chiral amine and thiourea structures were designed and synthesized and have been successfully applied in the conjugated additions of thiols to a,a-unsaturated imides and enones.The reactions got quantitative yields and the ee values were up to 84%. It is noteworthy that the a-asymmetric protonation (up to 43% ee) also could be achieved.The Michael addition between aromatic thiols and a,a-unsaturated carbonyl compounds isdescribed as follows:Works to further increase the enantioselectivity is under investigation in our laboratory.     

Do intramolecular halogen bonds exist? Ab initio calculations and crystal structures’ evidences

Cl···O intramolecular contacts are analysed here. Hence the Cambridge Structural Database (CSD) search was performed to find five-membered Cl–C=C–C=O pseudo-rings closed through Cl···O intramolecular contacts. Such rings were analysed and it was found that some of Cl···O distances are smaller than the corresponding sum of van der Waals radii. Additionally ab initio MP2/6-311++G(d,p) calculations and AIM analyses were carried out here on 3-chloropropenal and its fluoro derivatives to deepen the nature of intramolecular Cl···O interactions, some of findings may indicate that they are attractive and stabilizing ones. This paper is dedicated to Prof. T. M. Krygowski on the occasion of his 70th birthday     

氯化钠在球形纳米氧化铈形成过程中的作用

以水合碳酸铈为原料, 以氯化钠作为助磨剂和阻聚剂, 采用机械活化法制备了球形纳米氧化铈, 用XRD法研究了水合碳酸铈与氯化钠质量比、球磨时间、煅烧温度对CeO2粉体晶粒度的影响, 用TEM对最终产物粒子进行形貌观察. 结果表明: 在碳酸铈的球磨过程及其随后的煅烧过程中, 氯化钠的存在起到了很好的助磨和阻聚作用, 所得CeO2为类球形粒子, 分散性较好, 晶粒度约为30～50 nm.     

Non-isothermal kinetics of dehydration of equilibrium swollen poly(acrylic acid) hydrogel</o:p>

Summary Kinetics of dehydration of equilibrium swollen poly(acrylic acid) hydrogel was investigated using methods of non-isothermal thermal analysis. Methods of Kissinger, Coats-Redfern, Van Krevelen and Horowitz-Metzger were applied for determination the kinetics parameters: activation energy (E), pre-exponent (lnA) as well as the kinetics model ƒ(69) for the process of hydrogel dehydration under different heating rates. An existence of good agreement between determined values of kinetic parameters (Eand A), which were obtained applying different methods under the same heating rate. Functional relationship between changes of kinetic parameters of dehydration and changes of heating rate was established. An existence of compensation effect is accepted and explanation of compensation effect appearance during the hydrogel dehydration is suggested.     

The Role of γ -Aminopropyltriethoxysilane (γ -APS) on Thermal Stability of TEOS-PDMS Ormosils

The degradation process of TEOS-PDMS Ormosils containing different amounts of γ -APS has been studied by means of DTA, TG, FTIR and ²⁹Si-NMR measurements. It has been found that the amount of γ -APS improved the thermal properties of Ormosil materials. The increase in γ -APS content causes the increment on the decomposition temperatures and activation energies of the studied Ormosils. These results have been attributed to the favourable effect of γ -APS in the copolymerisation reaction between TEOS and PDMS molecules. ²⁹Si-NMR analyses have shown that the incorporation of γ -APS increases the concentration of D(Q) units in the Ormosil structure, i.e., increases the number of TEOS molecules bonded to PDMS ones. Initial decomposition temperature (IDT), temperature of maximum weight loss rate (T_max), integral procedure decomposition temperature (IPDT) and activation energy values (E) were calculated from different equations which described the degradation of these materials. Addition of 10 wt% γ -APS produced an increase of 63^∘C in the IDT and of 115 and 110^∘C, respectively, for T_max and IPDT (up to 478 and 610^∘C) compared to the free γ -APS Ormosil. Activation energy values also rise up to 69.4 kJ⋅ mol⁻¹ by introducing 10 wt% of γ -APS.     

Chemical thermodynamics

The curing of composition containing epoxy bond is complicated chemical and technological process where under temperature and pressure conditions a change of its structure occurs. The structure changes are possible to know by thermal methods as DSC, DTA, etc. and also by measurement of dielectrical response under the low frequency electrical field.     

配合物形成的三维超分子体系—[Ni(C_6H_4O_2N)_2(H_2O)_4]的水热法合成、晶体结构及热分析

采用水热法用Ni(NO3)26H2O和异烟酸制备出了一种新的由配合物形成的三维超分子体系—[Ni(C6H4O2N)2(H2O)4],并通过X射线衍射对其晶体结构进行了测定。 该晶体属三斜晶系,空间群为Pī, 所得晶胞参数为: a = 6.9228(4), b = 9.6664(19),c = 6.322(1) , a = 96.86(3), b = 113.33(3), g = 110.35(3)°, V = 347.6(1) 3, Z = 1, Mr = 374.98, Dc = 1.791 g/cm3, F(000) = 194, m = 1.443 mm-1。用1362个可观察的 (I > 2s(I))衍射点,修正123个结构参数, 最终偏离因子R = 0.0444,wR = 0.1271。在组成该化合物的基本结构单元[Ni(C6H4O2N)2(H2O)4]中,Ni处于1个稍微拉长的八面体的中心; 各个结构单元之间通过氢键OH…O相互连接,形成了无限伸展的具有层状结构的三维超分子体系。 另外,从差热及热重曲线可以看出,该化合物加热到154 ℃时开始分解, 首先失去4个H2O,再失去2个异烟酸根,最后残余物为NiO。     

3D Supramolecular Network Based on Hydrogen Bonds Between 1D [ Ni（μ2-C2O4） （ Him）2] Zigzag Chains

Introduction In recent years,considerable attention has been paid to supramolecular networks based on metal organic building blocks because of their potential applications in diverse fields,such as,catalysis,optics,sensors, magnetism,and molecular recognition[1-3].On the ba-     

Existence of aromatic sp~2 C-H…O = C intramolecular interaction similar to hydrogen bond

A 'H NMR signal shifted drastically to down field (δ - 10.0) at the bay area and in dose proximity to C = O group for H-1 was observed through complete assignments of 1H NMR spectra for pyridino- and benzobenzanthrones. It is concluded that this phenomenon is due not only to the anisotropy effect of C=O plus aromatic ring current effect, but also to the electrostatic attraction of C-H (δ+)…O(δ-)=C interaction. The evidence for the sp2C-H…O = C intramolecular interaction similar to hydrogen bond has also been given by EI-MS and MS/MS (CID) spectroscopy and IR spectroscopy, as well as MNDO-PM3 calculations. This new kind of interaction might be called 'quasi-hydrogen bond'.