SYNTHESIS AND PROPERTIES OF POLYMERIC BIS (ETHYLENEDITHIO)-TETRATHIAFULVALENES

A polymer containing bis(ethylenedithio)-tetrathiafulvalene moiety wassynthesized and its electrochemical properties were studied by cyclic voltammetry. Thecharge transfer complexes of the polymer with TCNQ and I_2 were obtained by chemicaloxidation in dichlorobenzene. All of them are semi-conductors. A film of the polymer wasobtained by casting. Its conductivity, after oxidation with iodine, is 2.24×10~(-6)S·cm~(-1)and its conducting state is stable in air.     

影响轻钢龙骨轻质板隔墙的隔声性能的因素

单层墙体因受质量定律的限制，必须是重墙才能获得良好的隔声性能。     

局部调整法解趣题

为了解决一个问题,或者解一道数学题,有时可以通过对问题中的一部分量进行有限次调整,让其它对象暂时不变,得出局部结果之后,再做进一步调整和研究(有时是重复性的调整),从而缩小范围,最终得到整个问题的圆满解决,这种思维方法就叫局部调整法.著名的几何学家斯坦纳在《等周问题与轴对称》一文中也就是用了这种“局部调整法”证     

Synthesis and Crystal Structure of N3-（Dimethyl- pyrimidine）-N4-（tri-O-acetyl-xylosyl） Thiourea

The crystal structure of the title compound （C18H24N4O7S, Mr = 440.47） was prepared by the condensation of 2,3,4-tri-O-acetyl-β-D-xylopyranosyl isothiocyanate with 4,6-dimethylpyrimidin-2-amine and structurally determined by single-crystal X-ray diffraction. The crystal belongs to the monochnic system, space group P2 1 with a = 7.5500（17）, b = 10.498（2）, c = 14.208（3） A, β = 99.929（4）°, V = 1109.2（4） A^3, Z = 2, Dc = 1.319 g/cm^3,μ = 0.191, F（000） = 464, Flack = 0.00（15）, R = 0.0684 and wR = 0.1103. In the crystal structure, the xylose ring adopts a ^4C1 chair conformation. Due to the hydrogen bonding interaction between N（4）-H（4A） and N（1）, the pyrimidine ring is well positioned.