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相关概念视频

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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相关实验视频

Updated: Feb 16, 2026

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

Published on: April 10, 2018

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在单原子基异质催化剂上的C-C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
概括
此摘要是机器生成的。

这项研究引入了一种基于单个原子 (Pd1/TiO2) 的基于TiO2的新型纳米粒子催化剂,用于高效的SonogashiraC-C合反应. 这种异质催化剂具有高活性和易于分离,克服了传统同质催化剂的局限性.

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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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Multiscale Sampling of a Heterogeneous Water/Metal Catalyst Interface using Density Functional Theory and Force-Field Molecular Dynamics

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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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Multiscale Sampling of a Heterogeneous Water/Metal Catalyst Interface using Density Functional Theory and Force-Field Molecular Dynamics

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科学领域:

  • 不同质的催化
  • 纳米粒子催化
  • 有机金属化学

背景情况:

  • 同质的C-C合催化面临着催化剂分离和成本的挑战.
  • 开发高效的异质催化剂对于可持续的化学合成至关重要.
  • 二氧化 (TiO2) 是催化剂支的多功能材料.

研究的目的:

  • 开发一种高活性且可重复使用的异质催化剂,用于Sonogashira的C-C合反应.
  • 研究单原子对TiO2纳米粒子的催化性能.
  • 通过密度函数理论 (DFT) 的计算来阐明反应机制.

主要方法:

  • 基于TiO2的纳米粒子催化剂的合成,单独散的Pd原子 (Pd1/TiO2).
  • 测试催化剂的活性和选择性超过10 Sonogashira C-C 合反应.
  • 执行DFT计算以了解原子层次的反应机制.

主要成果:

  • 在超过10个Sonogashira合反应中,Pd1/ TiO2表现出高活性和选择性.
  • 在60°C时,每分钟达到每Pd原子51.0个乙烯分子的转换率.
  • 在没有催化剂分离成本的情况下,观察到28.9kJ/mol的低明显激活屏障.

结论:

  • 在TiO2纳米粒子上的单原子 (Pd1/TiO2) 是Sonogashira C-C合的有效异质催化剂.
  • 催化剂有助于高效的C-C键形成,易于分离和重复使用.
  • DFT计算显示了一种机制,涉及Pd1上吸附的基中间体和TiO2上的基乙.