共查询到19条相似文献,搜索用时 62 毫秒
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Cram经验规则在判断与手性中心相连羰基的亲核加成立体选择性方面具有重要应用,目前教材常采用Newman投影式结合Cram规则进行主要产物的预测,而当Cram规则使用于其他构象表示式如锯架式、伞形式及Fischer投影式时,需要先进行构象转换,这对学生的空间想象能力及抽象思维提出较高要求,导致在判断时容易出错,是有机化学学习的一个难点。通过对Cram规则的深入分析,介绍Cram规则如何直接应用于除Newman表示式外的常用构象表示式,以避免费时费力又容易出错的构象式转化。 相似文献
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分享了一种巧用左手手势,结合一首五言口诀快速判断糖分子结构的方法。口诀为:“罗卓葡古塔,甘露艾半乳。核阿木来苏,酮糖果山古”,包含了常见的12种醛糖和6种酮糖。通过该方法,不仅能快速准确写出各种常见糖的Fischer投影式,而且还可应用于糖分子相应的Haworth透视式及椅式构象,值得在糖类教学中进行推广。 相似文献
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通过总结归纳4种立体结构表达式(楔形透视式、锯架透视式、纽曼投影式、费歇尔投影式)的书写特点,对含两个不同手性碳的有机分子结构式提出主键和共平面概念,并以此为主线,得到了4种立体结构式之间相互转换方法的一般规律。 相似文献
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用SDS-PAGE法研究了酸溶胶原中的α1,α2,β11,β12组份在中性水溶液以及加入盐(AuCl3等)后的水解能力。实验表明:在水溶液中,α1与α2的水解能力相近,β11与β12的水解能力也相差不多。但在加入与乳剂成熟条件一致的金属盐[AuCl3(0.167‰,NH4CNS(2‰)和Na2S203(1‰)]之后,由于金属离子(尤其是Au3+)的影响,α1的水解能力明显大于α2,β11的水解能力明显大于β12.本文还讨论了影响胶原中不同组份水解能力的各种因素。 相似文献
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运用密度泛函理论(DFT) UB3LYP和有限场(FF)方法, 探讨了6,6’-二氧-3,3’-二四联氮自由基及其衍生物构象变化对非线性光学性质的影响, 分析了自由基分子极化率、二阶超极化率对构象、自旋多重度的依赖关系. 结果表明, 不同构象下各体系有效交换积分值都小于零, 自由基间表现为反铁磁性耦合. 各体系单三态不同构象时极化率α值的变化很小, 且不同构象时单重态的α值都大于三重态. 在构象变化过程中, 体系(a)和(b)单重态的二阶超极化率均为负值(体系(a)的45°和135°除外), 且绝对值都小于三重态的二阶超极化率值, 体系(c)的单三重态二阶超极化率值均为正值, 且在分子接近平面构型时, 三重态的γ值大于单重态. 不同的取代基R, 对体系的构型、极化率和二阶超极化率的影响也不同. 相似文献
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使用分子动力学模拟迟火和半经验AMl方法对谷胱甘肽分子伞进行了构象分析 ,结果表明,真空下屏蔽构象和暴露构象的最低能量值相差很小(26.00kJ/mol)。 考虑溶剂效应后,屏蔽构象的能量值最高,暴露构象的能量值最低。屏蔽构象的能 量最低值高于暴露构象的能量最低值89.24kJ/mol,从理论上解释了谷胱甘肽分子 伞在水溶液中呈现暴露构象的原因。利用VolSurf参数分析了分子伞以屏蔽构象穿 透磷脂双分子层的影响因素,结果表明屏蔽构象较小的两亲矩及较大的分子褶皱程 度是其能够穿透细胞膜的主要影响因素,与构象的绝对疏水区域无关。 相似文献
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The chemical components and medicinal properties of different medicinal parts of Angelica sinensis are often used as medicine after being divided into the head, body and tail of Angelica sinensis. In this study, the chemical components of different medicinal parts in different periods were analyzed by GC-MS for the first time, and the differences of the accumulation rules of chemical components in different medicinal parts of Angelica sinensis were obtained. This study demonstrated that the differences of composition accumulation in different medicinal parts of Angelica sinensis were mainly reflected in the types and relative contents of compounds. The study found that the number of compounds in different medicinal parts of Angelica sinensis in each period were different and the change rules of the same compound in different medicinal parts were also different. The number of compounds in the tail of Angelica sinensis was the least in April, and the largest in October. The content of ligustilide in the body of Angelica sinensis was higher in April and was the highest in the tail in October. The relative content of butylidenephthalide in the head was the highest in October. The relative contents of senkyunolide A and butylphthalide in the head were decreased in October, while the contents in the body and tail increased, indicating that the compounds that accumulate in the head may transfer to the body and tail in later stages of growth. This study clarified the differences in the accumulation of chemical components in different medicinal parts of Angelica sinensis, which could provide a theoretical basis for the reasons for the differences of chemical components in the different medicinal parts. 相似文献
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Prof. Dr. Li‐Hua Gan Jie An Prof. Fu‐Sheng Pan Qing Chang Prof. Zuo‐Hua Liu Prof. Chang‐Yuan Tao 《化学:亚洲杂志》2011,6(6):1304-1314
The discovery of buckminsterfullerene C60 opened up a new scientific area and stimulated the development of nanoscience and nanotechnology directly. Fullerene science has since emerged to include fullerenes, endohedral fullerenes (mainly metallofullerenes), exofullerenes, and carbon nanotubes as well. Herein, we look back at the development of fullerene science from the perspective of epistemology by highlighting the proposed main rules or criteria for understanding and predicting the structures and stability of fullerene‐based compounds. We also point out that a rule or criterion may contribute significantly to the corresponding discipline and suggest that two unsolved issues in fullerene science are the addition patterns of fullerene derivatives and the structures and stability of nonclassical fullerenes. 相似文献
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介绍了我国食品营养强化剂使用卫生标准,特别是对其中一些重要备注和规定进行了归纳和说明. 相似文献
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Homo- and heteronuclear bimetallic carbene complexes of group VII transition metals (Mn and Re), with cymantrene or cyclopentadienyl rhenium tricarbonyl as the starting synthon, have been synthesized according to classic Fischer methodology. Crystal structures of the carbene complexes with general formula [RC5H4 M'(CO)2{C(OEt)(C5H4 M(CO)3)}], where M = M′ = Mn, R = H (1), R = Me (2); M = Mn, M′ = Re, R = H (3); M = M′ = Re, R = H (4); and M = Re, M′ = Mn, R = H (5), are reported. A density functional theory (DFT) study was undertaken to determine natural bonding orbitals (NBOs) and conformational as well as isomeric aspects of the binuclear complexes. Application of second-order perturbation theory (SOPT) of the NBO method revealed stabilizing interactions between the methylene C–H bonds and the carbonyl ligands of the carbene metal moiety. Energy calculations in the gas phase of the cis and trans conformations of the Cp rings relative to one another are comparable, with the trans conformation slightly lower in energy. The theoretical findings have also been confirmed with single-crystal X-ray diffraction, and all solid-state structures are found in the trans geometry. 相似文献
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药物分子设计中的Lipinski规则 总被引:1,自引:0,他引:1
Lipinski规则是药物分子设计和药物筛选中常用的规则之一。本文从它的形成出发,举例说明了它在先导化合物的结构优化和药物筛选等方面的效用;同时,还指出了此规则的使用范围及其局限性,旨在人们能够正确认识和恰当应用它。 相似文献
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中孔分子筛HMS负载钴催化剂在费-托合成中的应用:载体HMS的孔径对钴基催化剂性能的影响 总被引:9,自引:1,他引:9
用不同链长度的十二胺,十四胺,十六胺和十八胺等伯胺为模板\r\n剂合成了具有不同孔径大小的HMS中孔分子筛.XRD和低温氮吸附测定表\r\n明,HMS具有典型的中孔分子筛特征,且其孔径大小随HMS合成中所用模\r\n板剂链长度的增加而增加.以HMS为载体,采用孔体积浸渍法制备了负\r\n载量为7.5%的钴催化剂,在接近工业试验条件下(n(H2)/n(CO)\r\n=2.1,GHSV=500h-1,p=2.0MPa,θ=227℃)考察了载体孔径大\r\n小对费-托合成反应性能的影响.结果表明,与常规的SiO2载体相比,\r\nHMS负载钴催化剂具有更高的催化活性和C5+选择性;而且,CO转化率\r\n,C5+选择性及产物中的蜡油比均随着HMS载体孔径的增大而升高.以\r\n7.5%Co/HMS-18为催化剂,CO转化率为78.0%,C5+选择性为80.\r\n8%,蜡油比为11.1. 相似文献