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Related Concept Videos

Atomic Nuclei: Nuclear Relaxation Processes01:23

Atomic Nuclei: Nuclear Relaxation Processes

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In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis,  the precessing magnetic moments are randomly oriented around the z-axis.
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Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

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

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

1.2K
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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Atomic Nuclei: Nuclear Spin State Overview01:03

Atomic Nuclei: Nuclear Spin State Overview

1.1K
NMR-active nuclei have energy levels called 'spin states' that are associated with the orientations of their nuclear magnetic moments. In the absence of a magnetic field, the nuclear magnetic moments are randomly oriented, and the spin states are degenerate. When an external magnetic field is applied, the spin states have only 2 + 1 orientations available to them. A proton with = ½ has two available orientations. Similarly, for a quadrupolar nucleus with a nuclear spin value of...
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¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

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Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
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π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds01:14

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1.3K
In aromatic compounds, such as benzene, the circulation of (4n + 2) π-electrons sets up a diamagnetic or diatropic ring current around the perimeter of the molecule. This current induces a magnetic field that opposes the external field inside the ring and reinforces it on the outside. The protons in benzene are deshielded and exhibit high chemical shifts in the range 6.5–8.5 ppm. The shielding effect at the center of the ring is evident in complex aromatic molecules, such as...
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Experimental Methods for Spin- and Angle-Resolved Photoemission Spectroscopy Combined with Polarization-Variable Laser
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Frustration-Induced Many-Body Degeneracy in Spin -1/2 Molecular Quantum Rings.

Donglin Li1, Nan Cao2, Marvin Metzelaars3,4

  • 1Center for Basic Research on Materials, National Institute for Materials Science, 1-2-1 Segen, Tsukuba, Ibaraki 305-0047, Japan.

Journal of the American Chemical Society
|July 11, 2025
PubMed
Summary
This summary is machine-generated.

Researchers created frustrated spin systems using molecular rings. These systems exhibit unique quantum properties due to geometric frustration, offering new ways to control quantum magnetism.

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Area of Science:

  • Condensed Matter Physics
  • Quantum Chemistry
  • Materials Science

Background:

  • Frustrated spin systems exhibit competing magnetic interactions, preventing conventional ordering and enabling exotic quantum phenomena.
  • Low-dimensional and symmetric molecular geometries are crucial for studying unconventional spin states without boundary effects.

Purpose of the Study:

  • To synthesize and characterize S = 1/2 antiferromagnetic Heisenberg cyclic pentamer and hexamer molecular systems.
  • To investigate the impact of geometric frustration on quantum spin states and magnetic interactions.

Main Methods:

  • Homocoupling of air-stable phenalenyl derivatives on a gold(111) surface.
  • Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) at low temperatures (4.3 K).
  • Comprehensive theoretical simulations to analyze magnetic exchange interactions and spin wave functions.

Main Results:

  • Successful synthesis of cyclic pentamer and hexamer spin systems with large magnetic exchange interactions.
  • Pentamer systems exhibit increased geometric frustration, leading to rotational symmetry in spin wave functions.
  • A 4-fold degenerate ground state was observed in the pentamer system due to geometric frustration.

Conclusions:

  • The interplay between molecular geometry and magnetic interactions in these systems creates a unique quantum spin environment.
  • This work provides a method for constructing spin-frustrated molecular architectures with controlled quantum magnetic interactions.
  • Findings pave the way for novel applications in quantum computing and spintronics.