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Related Concept Videos

Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

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

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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...
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¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

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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...
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NMR Spectroscopy: Spin–Spin Coupling01:08

NMR Spectroscopy: Spin–Spin Coupling

1.3K
The spin state of an NMR-active nucleus can have a slight effect on its immediate electronic environment. This effect propagates through the intervening bonds and affects the electronic environments of NMR-active nuclei up to three bonds away; occasionally, even farther. This phenomenon is called spin–spin coupling or J-coupling. Coupling interactions are mutual and result in small changes in the absorption frequencies of both nuclei involved. While nuclei of the same element are involved...
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Spin–Spin Coupling: One-Bond Coupling01:17

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951
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,...
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¹³C NMR: ¹H–¹³C Decoupling01:04

¹³C NMR: ¹H–¹³C Decoupling

1.1K
The probability of having two carbon-13 atoms next to each other is negligible because of the low natural abundance of carbon-13. Consequently, peak splitting due to carbon-carbon spin-spin coupling is not observed in spectra. However, protons up to three sigma bonds away split the carbon signal according to the n+1 rule, resulting in complicated spectra.
A broadband decoupling technique is used to simplify these complex, sometimes overlapping, signals. Broadband decoupling relies on a...
1.1K
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

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985
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...
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Machine Learning Big Data Set Analysis Reveals C-C Electro-Coupling Mechanism.

Haobo Li1, Xinyu Li2, Pengtang Wang1

  • 1School of Chemical Engineering, the University of Adelaide, Adelaide SA 5005, Australia.

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|August 3, 2024
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Summary
This summary is machine-generated.

This study reveals asymmetric carbon-carbon coupling is more efficient for CO2 reduction. Copper-silver-niobium (CuAgNb) catalysts boost selectivity, offering a new paradigm for green chemical production via big data and machine learning.

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Area of Science:

  • Catalysis
  • Electrocatalysis
  • Green Chemistry
  • Materials Science
  • Computational Chemistry

Background:

  • Carbon-carbon (C-C) coupling is crucial for electrocatalytic CO2 reduction to green chemicals.
  • Reaction mechanisms and catalyst design for C-C coupling remain complex and debated.
  • A comprehensive dataset and advanced analysis are needed to understand and optimize C-C coupling.

Purpose of the Study:

  • To establish a comprehensive dataset of C-C coupling precursors and active site compositions.
  • To explore reaction mechanisms and screen catalysts using big data analysis.
  • To accelerate catalyst design for efficient CO2 electroreduction.

Main Methods:

  • Developed a 2D-3D ensemble machine learning strategy to expand quantum chemical calculation data.
  • Generated an extensive big dataset encompassing C-C coupling precursors and active site compositions.
  • Analyzed the dataset to identify optimal reaction pathways and catalyst compositions.

Main Results:

  • Asymmetric coupling mechanisms (e.g., CHO with CH or CH2) show higher potential efficiency than symmetric ones.
  • Bimetallic doping of Cu-based catalysts, specifically CuAgNb sites, enhances C-C coupling selectivity.
  • Experimental validation confirmed that CuAgNb catalysts significantly boost C-C coupling performance.

Conclusions:

  • Big data analysis, accelerated by machine learning, provides practical insights into complex catalytic systems.
  • Asymmetric coupling pathways and tailored bimetallic catalysts represent promising directions for CO2 electroreduction.
  • Combining big data with computational chemistry and experimental validation establishes a new paradigm for catalyst design.