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相关概念视频

Nuclear Transmutation03:20

Nuclear Transmutation

Nuclear transmutation is the conversion of one nuclide into another. It can occur by the radioactive decay of a nucleus, or the reaction of a nucleus with another particle. The first manmade nucleus was produced in Ernest Rutherford’s laboratory in 1919 by a transmutation reaction, the bombardment of one type of nuclei with other nuclei or with neutrons. Rutherford bombarded nitrogen-14 atoms with high-speed α particles from a natural radioactive isotope of radium and observed protons being...
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The addition of a hydrogen halide to 1,3-butadiene gives a mixture of 1,2- and 1,4-adducts. Since more substituted alkenes are more stable, the 1,4-adduct is expected to be the major product. However, the product distribution is strongly influenced by temperature; low temperature favors the 1,2-adduct, whereas the 1,4-adduct is predominant at high temperature.
Radical Reactivity: Steric Effects01:10

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The presence of electron-donating, electron-withdrawing, or conjugating groups adjacent to a radical center, imparts electronic stabilization to the radicals. Examples of such electronically-stabilized radicals are triphenylmethyl, tetramethylpiperidine‐N‐oxide, and 2,2‐diphenyl‐1‐picrylhydrazyl. These radicals are remarkably stable and are known as persistent radicals. Some of the persistent radicals can even be isolated and purified.
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Irradiation of a spin-active nucleus causes an increase or decrease in the signal intensity of neighboring nuclei that are not necessarily chemically bonded or involved in J-coupling. This phenomenon, called the nuclear Overhauser enhancement (NOE), results from through-space interactions between the nuclear spins. The NOE effect decreases with increasing internuclear distance and is generally not observed beyond 4 angstroms. In NOE, dipole-dipole interactions between neighboring spin-active...
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原子转移激素聚合中的激素陷不需要热力学稳定. 关于MoX(3)(PMe(3)) 的催化剂的一项研究.

Sébastien Maria1, François Stoffelbach, José Mata

  • 1Laboratoire de Chimie de Coordination, UPR CNRS 8241, 205 Route de Narbonne, 31077 Toulouse Cedex, France.

Journal of the American Chemical Society
|April 21, 2005
PubMed
概括

(III) 复合物通过原子转移基聚合 (ATRP) 控制烯聚合. 化物复合物的氧化还原不稳定性是它们的基因捕获机制的关键,影响了聚合控制.

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科学领域:

  • 协调化学 协调化学
  • 聚合催化法 聚合催化法
  • 有机金属化学 有机金属化学

背景情况:

  • 原子转移基聚合 (ATRP) 是一种受控聚合技术.
  • (III) 复合物被探索为ATRP的催化剂.
  • 了解自旋陷的作用对于控制激进聚合是至关重要的.

研究的目的:

  • 为了研究聚合物聚合中 ((III) 协调复合物的催化活性.
  • 通过使用电化学和合成方法,阐明这些复合物捕捉基因的机制.
  • 为了确定化物联体 (Cl,Br,I) 对催化性能和氧化还原稳定性的影响.

主要方法:

  • 使用MoX(3)(PMe(3)) ((3)) (X=Cl, Br, I) 和2-甲开启器的烯的原子转移基聚合 (ATRP).
  • 电化学研究,包括循环电压测量,以探测氧化还原行为.
  • 合成研究涉及氧化复合物和结构特征 (X射线晶体学).

主要成果:

  • (III) 复合物通过ATRP有效控制烯聚合,由Al (OPr (i)) (iii)) 协催化剂加速.
  • 电化学研究显示,氧化反应的可逆性增加,其顺序为Cl < Br < I.
  • 化物复合物表现出氧化还原不稳定性,特别是MoI(3) X((PMe(3)) ((3),这表明它们作为激素捕获物种的作用.
  • 氧化MoI ((3)) ((PMe ((3)) ((3)) 产生一种氧化还原不稳定的四多摩酸 ((III) 盐,这种盐缺乏聚合控制.

结论:

  • (III) 复合物,特别是衍生物,可以催化和控制烯ATRP.
  • 含有的基物种的氧化还原不稳定性对于它们作为ATRP中的激素陷的功能至关重要.
  • 化物交换和氧化途径显著影响这些复合物的催化活性和稳定性.