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Related Concept Videos

Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

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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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NMR Spectroscopy: Spin–Spin Coupling01:08

NMR Spectroscopy: Spin–Spin Coupling

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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

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)

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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 involved orbitals. The...
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Atomic Nuclei: Nuclear Spin01:08

Atomic Nuclei: Nuclear Spin

5.1K
All atomic particles possess an intrinsic angular momentum, or 'spin'. Electrons, protons, and neutrons each have a spin value of ½, although protons and neutrons in nuclei may have higher half-integer spins owing to energetic factors.
Atomic nuclei have a net nuclear spin, , which can have an integer or half-integer value. In atomic nuclei, the spins of protons are paired against each other but not with neutrons, and vice versa. Consequently, an even number of protons does not contribute to...
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The spin structure of the nucleon.

Alexandre Deur1, Stanley J Brodsky2, Guy F de Téramond3

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The spin structure of protons and neutrons is more complex than previously thought, involving quark orbital angular momenta and gluon contributions. Advances in Quantum Chromodynamics (QCD) and new theoretical frameworks are crucial for understanding nucleon spin.

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Area of Science:

  • Nuclear Physics and Particle Physics
  • Quantum Chromodynamics (QCD)
  • Hadron Structure

Background:

  • Nucleons (protons and neutrons) are fundamental to nuclear structure.
  • The spin structure of nucleons is a key area for testing Quantum Chromodynamics (QCD).
  • Early models incorrectly assumed nucleon spin primarily derived from quark spins.

Purpose of the Study:

  • To review the current understanding of nucleon spin structure.
  • To highlight the complexity beyond simple quark spin contributions.
  • To discuss experimental and theoretical advances in probing nucleon spin.

Main Methods:

  • Analysis of deep inelastic lepton scattering experiments with polarized targets.
  • Theoretical developments including generalized parton distributions (GPDs) and transverse momentum distributions (TMDs).
  • Exploration of non-perturbative QCD using elastic/inelastic lepton scattering and photoabsorption.
  • Application of lattice gauge theory simulations and holographic QCD (AdS/CFT correspondence).
  • Utilizing light-front holography and superconformal quantum mechanics for analytic calculations.

Main Results:

  • Nucleon spin arises from a complex interplay of quark spins, orbital angular momenta, and gluon contributions.
  • Experimental and theoretical efforts have revealed the inadequacy of simple parton model predictions.
  • New theoretical frameworks like GPDs, TMDs, and holographic QCD offer deeper insights into nucleon structure.
  • Analytic calculations of hadron spectra are now achievable, consistent with nucleon spin studies.

Conclusions:

  • Nucleon spin structure is a dynamic research frontier in QCD.
  • Understanding nucleon spin requires incorporating orbital angular momenta and gluon dynamics.
  • Advanced theoretical tools and experimental data are essential for a complete picture of hadron structure.