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Related Concept Videos

Atomic Nuclei: Nuclear Spin State Overview01:03

Atomic Nuclei: Nuclear Spin State Overview

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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 one, the...
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Spin–Spin Coupling: One-Bond Coupling01:17

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

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1.4K
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...
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Spin–Spin Coupling Constant: Overview01:08

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

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

1.5K
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...
1.5K
The Pauli Exclusion Principle03:06

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The arrangement of electrons in the orbitals of an atom is called its electron configuration. We describe an electron configuration with a symbol that contains three pieces of information:
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Updated: Dec 30, 2025

Experimental Methods for Spin- and Angle-Resolved Photoemission Spectroscopy Combined with Polarization-Variable Laser
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Spin-flip methods in quantum chemistry.

David Casanova1, Anna I Krylov2

  • 1Donostia International Physics Center (DIPC), 20018 Donostia, Euskadi, Spain. david.casanova@ehu.eus and IKERBASQUE, Basque Foundation for Science, 48013 Bilbao, Euskadi, Spain.

Physical Chemistry Chemical Physics : PCCP
|January 23, 2020
PubMed
Summary
This summary is machine-generated.

The spin-flip approach offers a novel way to study strong correlation by leveraging differences between low-spin and high-spin states. This method enhances calculations for molecular properties and spectroscopy.

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Area of Science:

  • Quantum Chemistry
  • Computational Physics
  • Strong Correlation Physics

Background:

  • Strong correlation poses challenges in electronic structure calculations.
  • Traditional methods struggle with accurately describing low-spin states.

Purpose of the Study:

  • To discuss the spin-flip approach for strong correlation.
  • To review methods derived from the spin-flip concept.
  • To highlight applications in molecular properties and spectroscopy.

Main Methods:

  • Exploits the physics of low-spin and high-spin states.
  • Uses high-spin states as a reference for low-spin states.
  • Applies formal tools from excited-state theories (linear response, propagator, equation-of-motion).

Main Results:

  • Spin-flip methods provide access to problematic low-spin states.
  • The approach is applicable within wave function and density functional theory.
  • Demonstrated utility in calculating molecular properties and spectroscopy.

Conclusions:

  • The spin-flip approach is a valuable strategy for tackling strong correlation.
  • It offers extensions for molecular properties and spectroscopic investigations.
  • Future directions and limitations are also considered.