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Related Concept Videos

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

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

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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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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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Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

959
In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must...
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¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

1.8K
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...
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Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

1.0K
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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NMR Spectroscopy: Spin–Spin Coupling01:08

NMR Spectroscopy: Spin–Spin Coupling

1.5K
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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Magnetic Coupling Control in Triangulene Dimers.

Hongde Yu1, Thomas Heine1,2,3

  • 1Faculty of Chemistry and Food Chemistry, Technische Universität Dresden, Bergstraße 66c, 01062 Dresden, Germany.

Journal of the American Chemical Society
|August 23, 2023
PubMed
Summary
This summary is machine-generated.

Researchers explored metal-free magnetism using triangulene dimers. They achieved strong antiferromagnetic coupling and realized ferromagnetic coupling in nitrogen-doped dimers, paving the way for new spintronic devices.

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Area of Science:

  • Materials Science
  • Quantum Chemistry
  • Condensed Matter Physics

Background:

  • Metal-free magnetism is crucial for novel electronic devices.
  • Triangulenes are promising organic monomers for spintronics due to inherent spin polarization.
  • Current limitations include weak magnetic coupling and lack of room-temperature applications.

Purpose of the Study:

  • Investigate magnetic coupling in triangulene dimers.
  • Enhance magnetic interactions for practical spintronic applications.
  • Explore strategies for controlling magnetic coupling strength and sign.

Main Methods:

  • First-principles calculations on 24 triangulene dimers.
  • Analysis of electronic structure and magnetic interactions.
  • Tuning molecular configurations (planar, twisted) and doping (nitrogen).

Main Results:

  • Achieved strong antiferromagnetic coupling (up to -144 meV, -198 meV in planar configurations).
  • Established correlation between bandgap, electronic coupling, and antiferromagnetic interaction.
  • Realized ferromagnetic coupling in nitrogen-doped triangulene dimers, defying the Ovchinnikov rule.

Conclusions:

  • Demonstrated tunable magnetic coupling in triangulene dimers through structural modification.
  • Provided molecular-level insights for enhancing magnetic interactions.
  • Opened new avenues for designing metal-free ferromagnets for spintronics.