Preparation and properties of a new polytype of tantalum disulfide (4Hb-TaS2)

A new polymorph of the layered compound tantalum disulfide, 4Hb-TaS₂, has been prepared in single crystal form. Measurements of magnetic susceptibility, electrical resistivity, and differential heat capacity show two first order transitions at 20 and 315°K. The 315°K transition involves only a small volume and enthalpy change, as in the previously observed transitions of another polymorph, 1T-TaS₂. The resistivity measurements show metallic like conductivity, as in 2H-TaS₂, when the current is parallel to the layers, but semiconducting like conductivity, as in 1T-TaS₂, when perpendicular to the layers. The properties of 4Hb-TaS₂ are moderately well described as a ‘mix’ of those of 1T-TaS₂ and 2H-TaS₂.     

Synthesis and conformational analysis of isomeric 3-propananilidotropanes

The isomeric 3-anilino and 3-propananilidotropanes have been synthesized and obtained in isomerically pure form. The configurations and solute conformations of these isomers were studied via glc and nrar analysis. The 3β-isomers have been shown to exist in the normal piper-idine chair conformation whereas the 3α-anilino tropane exists in a flattened piperidine chair conformation and the 3α-propananilidotropane isomer preferentially exists in a conformation in which the piperidine ring system is a boat.     

城市化进程中上海植被的多样性、空间格局和动态响应(Ⅷ):上海乡土陆生草本植物分布特征及其在城市绿化中的应用前景

通过相关资料查阅,建立了上海地区65科284属534种乡土陆生草本植物名录,并对大金山岛、佘山和上海市域“城区—城郊—郊县”城乡梯度上不同土地利用类型中野生草本植物的分布现状进行了调查,阐明了城市化影响下陆生草本植物的多样性格局.在分析物种的科属组成、地理成分、生活型和分布现状的基础上,阐明了地理位置、面积大小、生境类...     

T2紫铜与H62黄铜异种材料间的搅拌摩擦焊工艺研究

针对T2紫铜与H62黄铜异种材料进行了搅拌摩擦焊工艺研究.通过实验分析了不同板厚的紫铜和黄铜在各种工艺参数下的焊缝成形、接头微观组织及接头力学性能,并从微观角度分析了两种材料在接头中的分布情况及交界处的物相成分.实验表明,合适的焊接工艺参数可以获得组织、性能优良的紫铜-黄铜接头,接头交界处存在过渡带,宽度约为1~10μm的过渡物质.研究还发现接头显微硬度、平均抗拉强度介于黄铜与紫铜之间.     

Photoinduced oxygen transfer and double-linkage isomerism in a cis-(NO)(NO2) transition-metal complex by photocrystallography, FT-IR spectroscopy and DFT calculations

Photocrystallographic experiments show that laser exposure of crystals of [Ru(bpy)2(NO)(NO2)](PF6)2 at 90 K produces a double isonitrosyl-nitrito linkage isomer and provide the detailed geometry of the metastable species generated. The analysis indicates that the isomerization is accomplished through an intramolecular redox reaction involving oxygen transfer from the nitro to the nitrosyl group. At 200 K only a single (nitrito) linkage isomer is formed with a U-shaped conformation of the nitrito group rather than the Z conformation observed at 90 K. A mechanism for the isomerization is proposed based on the crystallographic results and FTIR data collected at low temperatures during the isomerization process. The study presents the first structural evidence for double linkage isomerization in transition-metal complexes.     

Barium manganate in microwave-assisted oxidation reactions: synthesis of lactones by oxidative cyclization of diols

Microwave irradiation of a range of diols at 150 °C in acetonitrile in the presence of three equivalents of barium manganate facilitates a novel tandem oxidation/heterocyclocondensation to give the corresponding lactone, including both small and medium ring lactones, in only one hour and in high yield without the need for chromatographic purification.     

三萜皂甙结构在2D NMR及化学反应中的研究进展

综述了近年来2DNMR技术在三萜皂甙结构研究中的新方法和经典的化学法,并通过相互比较,阐述了解析三萜皂甙结构较完善的研究方法。     

One-pot multistep Bohlmann-Rahtz heteroannulation reactions: synthesis of dimethyl sulfomycinamate

[reaction: see text] The synthesis of dimethyl sulfomycinamate, the acidic methanolysis product of the sulfomycin family of thiopeptide antibiotics, from methyl 2-oxo-4-(trimethylsilyl)but-3-ynoate is achieved in a 2,3,6-trisubstituted pyridine synthesis that proceeds with total regiocontrol in 13 steps by the Bohlmann-Rahtz heteroannulation of a 1-(oxazol-4-yl)enamine or in 12 steps and 9% yield by three-component cyclocondensation with N-[3-oxo-3-(oxazol-4-yl)propanoyl]serine and ammonia in ethanol.