Facial selectivity in the nucleophilic additions of vinylmagnesium bromide to bicyclo[2.2.2]oct-5-en-2-one derivatives

The levels of diastereoselection attainable by addition of vinylmagnesium bromide to a selection of bicyclo[2.2.2]octenone derivatives 1-6 in the presence of various Lewis acids such as LiBr, CeCl3, TiCl4, ZnBr2, MgBr2, and Et2AlCl have been determined. The 1,2-addition of ketone 1 with vinylmagnesium bromide in THF provided a mixture of anti- and syn-isomers. The reactions of 2 with vinylmagnesium bromide at room temperature afforded anti- and syn-isomers with preference to anti-isomers in most cases. These reactions in the presence of Lewis acids afforded anti-isomers as the major product with an excellent stereoselectivity or as single isomers in some cases. The ketones 3 gave surprisingly different results providing anti-isomers predominantly even in the presence of Lewis acids. The bicyclic ketones 4 and 5 and all-carbon tricyclic ketone 6 furnished the syn-isomer as the main product. There is no significant effect of Lewis acid catalysis in the nucleophilic addition reactions of 1, 4, 5, and 6. The use of a preformed vinylmagnesium bromide-CeCl3 reagent for the addition reactions of 2d-f and 3d-f provided almost exclusively syn-isomers. The substituents and reaction conditions can influence facial selectivity in the nucleophilic additions to the bicyclo[2.2.2]oct-5-en-2-one derivatives.     

NxHy-Fe(x=0～2,y=0～3)配位簇的DFT计算

采用杂化密度泛函（ＤＦＴ）之Ｂ３ＬＹＰ／６－３１１Ｇ＊＊方法研究了ＮｘＨｙ－Ｆｅ（ｘ＝０～２,ｙ＝０～３）配位簇的几何结构和振动光谱,讨论了在纯铁催化剂上,氮分子和氢分子逐步合成氨的反应机理,结果表明,合成氨过程可能经历Ｎ２和Ｎ２Ｈ２物种,在优化结构的基础上,计算了各个模型的振动频率并解释了有关实验结果。     

Luminescence Centers in BaFCl:Ce3+ and BaFCl:Gd3+ Crystals

Introduction In BaFCl crystal which is of PbFCl type structure in tetragonal system, Ba~(2+) ions situate at sites of C_(4?) point symmetry, while F~- and Cl~- ions occupy sites of D_(2d) and C_(4?) symmetry, respectively. The rare earth ions RE~(3+) doped in BaFCl should randomly replace the sites of Ba~(2+) ions, and their extra positive charges may be compensated by     

Stady on the Energy Spectra of fp Odd A Nuclei 47Ti,47V,49Cr With PDHF Method

The approximate angular momentum projected Hartree-Fock(PDHF)method is used to some odd-A nuclei in the fp shell:⁴⁷Ti,⁴⁷V,⁴⁷Cr,⁴⁹Cr.Their energy spectra are calculated and compared with the experimental data.The results are fairly satisfactory.In addition,the characteristics of those spectra are analyzed with the particle-rotor model.It is found that those spectra possess the properties of the no alignment limit Spectra.     

含吡啶基十四元六氮大环配体与Ni(Ⅱ)配合物的合成及性质的研究

金属四氮大环配合物的合成及性能的研究对于探讨生理过程,人工模拟具有一定的意义,本文研究的一种四氮配位的大环配合物是含有吡啶基的十四元四氮配位的大环配合物(图1),关于此类配合物的合成工作始于1974年,最早由Goedken和Paryzek合成了Fe(Ⅱ)、Mg(Ⅱ)、Zn(Ⅱ)、Sc(Ⅲ)的这类配合物。     

稀土化合物催化的Diels-Alder反应

Diels-Alder反应作为合成六元环化合物的一个主要方法,广泛用于有机合成中,特别是药物、香料及天然物质的合成。某些Diels-Alder反应需要较高的反应温度及压力。为了缓和反应条件,减少副反应,文献报道用路易斯酸(如AlCl₃、ZnCl₂等)作催化剂。     

Optical properties of nanocrystalline silicon embedded in SiO2

Nanocrystalline silicon embedded SiO₂ matrix has been formed by annealing the a-SiO_x films fabricated by plasma enhanced chemical vapor deposition technique. Absorption and photoluminescence spectra of the films have been studied in conjunction with micro-Raman scattering spectra. It is found that absorption presents an exponential dependence of absorption coefficient to photon energy in the range of 1.5–3.0 eV, and a sub-band appears in the range of 1.0–1.5 eV. The exponential absorption is due to the indirect band-to-band transition of electrons in silicon nanocrys-tallites, while the sub-band absorption is ascribed to transitions between surfaces and/or defect states of the silicon nanocrystallites. The existence of Stokes shift between absorption and photoluminescence suggests that the phonon-assisted luminescence would be enhanced due to the quantum confinement effects.     

硅胶-TBP 反相萃取层析分离法测定金(Ⅲ)与铊(Ⅲ) 的研究

以王水（体积分数为２０％）作移动相,以硅胶球负载的ＴＢＰ作固定相,反相萃取层析使微量Ａｕ（Ⅲ）、Ｔｌ（Ⅲ）与Ｆｅ３＋、Ｃｕ２＋、Ａｇ＋、Ｚｎ２＋、Ｍｎ２＋、Ｈｇ２＋、Ｃｄ２＋、Ｐｂ２＋、Ｓｂ５＋、Ａｓ５＋、Ｇａ３＋、Ｉｎ３＋、Ｐｔ２＋、Ｐｄ２＋等多种离子分离,留于柱上的铊、金分别用ＮａＡｃ溶液（量浓度为１ｍｏｌ／Ｌ）及Ｎａ２ＳＯ３溶液（质量浓度为１０ｇ／Ｌ）洗脱进行连续分离与测定（结晶紫光度法测定铊,孔雀绿光度法测定金）,回收率可达９６％以上,方法已应用于地质样品中金、铊的连续分离与测定。     

实用化双折射式光纤温度传感器系统最佳设计

利用双折射效应和偏振调制原理,设计了一种实用化的反射式光纤温度传感器,分析了精度、灵敏度等的主要指标与光源、双折射晶体及传输光纤之间的相互关系,并进行了相应的实验,给出了系统参数选择的最佳设计方案。     

非线性延时修正光纤孤子方程的稳态解问题Ⅱ.漂移型扭结孤波解

利用一种与Ｂｃｈｌｕｎｄ变换有关的方法严格求含非线性延时项光孤立子方程,得到了该方程的漂移型扭结孤波解,并讨论了解的极限性质和相关物理问题。最后指出了该方程在γ＝０处的参数不稳定性问题