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Catalysis02:50

Catalysis

30.8K
The presence of a catalyst affects the rate of a chemical reaction. A catalyst is a substance that can increase the reaction rate without being consumed during the process. A basic comprehension of a catalysts’ role during chemical reactions can be understood from the concept of reaction mechanisms and energy diagrams.
30.8K
¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

2.8K
The coupling interactions of nuclei across four or more bonds are usually weak, with J values less than 1 Hz. While these are usually not observed in spectra, the presence of multiple bonds along the coupling pathway can result in observable long-range coupling.
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene...
2.8K
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)

1.7K
Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
1.7K
Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

1.5K
Coupling interactions are strongest between NMR-active nuclei bonded to each other, where spin information can be transmitted directly through the pair of bonding electrons. While nuclei polarize their electrons to the opposite spins, the bonding electron pair has opposite spins. Configurations with antiparallel nuclear spins are expected to be lower in energy. When coupling makes antiparallel states more favorable, J is considered to have a positive value. The one-bond coupling constant, 1J,...
1.5K
Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)

1.5K
Vicinal or three-bond coupling is commonly observed between protons attached to adjacent carbons. Here, nuclear spin information is primarily transferred via electron spin interactions between adjacent C‑H bond orbitals. This generally favors the antiparallel arrangement of spins, so 3J values are usually positive.
The extent of coupling depends on the C‑C bond length, the two H‑C‑C angles, any electron-withdrawing substituents, and the dihedral angle between the involved orbitals. The...
1.5K
Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation02:24

Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation

9.1K
Introduction
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.
9.1K

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Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction
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Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction

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単原子基の異質な触媒のC−C結合

Xiaoyan Zhang1,2,3, Zaicheng Sun2, Bin Wang4

  • 1Department of Chemical Engineering and Department of Chemistry, University of Kansas , Lawrence, Kansas 66045, United States.

Journal of the American Chemical Society
|December 22, 2017
PubMed
まとめ
この要約は機械生成です。

この研究では,効率的なソノガシラC−C結合反応のために,単一のパラジウム原子 (Pd1/TiO2) を含む新しいTiO2ベースのナノ粒子触媒を導入しています. この異質な触媒は高い活性と容易な分離により,従来の同質な触媒の限界を克服します.

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Mizoroki-Heck Cross-coupling Reactions Catalyzed by Dichloro{bis[1,1',1''-phosphinetriyltripiperidine]}palladium Under Mild Reaction Conditions
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Multiscale Sampling of a Heterogeneous Water/Metal Catalyst Interface using Density Functional Theory and Force-Field Molecular Dynamics
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科学分野:

  • 異質な触媒
  • ナノ粒子触媒
  • 有機金属化学

背景:

  • 同質なC−C結合触媒は,触媒分離とコストの問題に直面しています.
  • 効率的な異質な触媒の開発は,持続可能な化学合成に不可欠です.
  • 二酸化チタン (TiO2) は,触媒のサポートのための多用途な材料です.

研究 の 目的:

  • Sonogashira C-C カップリング反応のための高度に活性で再利用可能な異質な触媒を開発する.
  • TiO2ナノ粒子に対する単原子パラジウムの触媒性能を調査する.
  • 密度関数理論 (DFT) の計算を用いて反応機構を解明する.

主な方法:

  • TiO2ベースのナノ粒子触媒の合成で,個別に分散したPd原子 (Pd1/TiO2) を固定する.
  • 10以上のソノガシラC-C結合反応で触媒の活性と選択性をテストした.
  • 原子レベルでの反応メカニズムを理解するためにDFT計算を実行します.

主要な成果:

  • Pd1/ TiO2は10以上のソノガシラ結合反応において高い活性と選択性を示した.
  • 60 °Cで分間にPd原子あたり51.0のディフェニルアセチレン分子の周回率を達成した.
  • 28. 9 kJ/molの低い明らかな活性化バリアが観察され,触媒分離コストはありませんでした.

結論:

  • TiO2ナノ粒子 (Pd1/TiO2) の単原子パラジウムは,ソノガシラC−C結合のための効果的な異質な触媒である.
  • 触媒は効率的なC−C結合を形成し,簡単に分離して再利用できます.
  • DFTの計算では,Pd1に吸収されたフェニル中間物質とTiO2に吸収されたフェニラセチレニルのメカニズムが明らかになった.