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Related Concept Videos

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

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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

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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.
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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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Valence Bond Theory02:42

Valence Bond Theory

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Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...
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Valence Bond Theory02:45

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Overview of Valence Bond Theory
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Site Directed Spin Labeling and EPR Spectroscopic Studies of Pentameric Ligand-Gated Ion Channels
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Spin-Delocalization in a Helical Open-Shell Hydrocarbon.

Prince Ravat1, Peter Ribar1, Michel Rickhaus1

  • 1Department of Chemistry, University of Basel , St. Johanns-Ring 19, 4056 Basel, Switzerland.

The Journal of Organic Chemistry
|November 5, 2016
PubMed
Summary
This summary is machine-generated.

This study explores spin-delocalized helical hydrocarbons, revealing how uneven electron distribution in naphtho[3,2,1-no]tetraphene influences selective dimerization. Steric hindrance prevents dimerization in substituted derivatives, confirming spin delocalization through chiral backbones.

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Area of Science:

  • Organic Chemistry
  • Materials Science
  • Magnetochemistry

Background:

  • Neutral open-shell molecules with delocalized spin density on helical backbones are key for studying magnetism-chirality interplay.
  • The chemical exploration of these compounds is limited, with few examples currently known.
  • Helically chiral open-shell hydrocarbons offer a unique platform for fundamental research.

Purpose of the Study:

  • To investigate spin-delocalization over a helical backbone in naphtho[3,2,1-no]tetraphene, a novel helically chiral open-shell hydrocarbon.
  • To understand how nonuniform spin distribution affects molecular behavior, specifically dimerization.
  • To validate spin delocalization through a chiral backbone using spectroscopic and computational methods.

Main Methods:

  • Synthesis and characterization of naphtho[3,2,1-no]tetraphene and its substituted derivatives.
  • 2D NMR spectroscopy to study σ-dimer formation in solution.
  • Electron Paramagnetic Resonance (EPR), UV-vis, and Circular Dichroism (CD) spectroscopies for characterization.
  • Density Functional Theory (DFT) calculations to rationalize spin distribution and aromaticity.

Main Results:

  • The unpaired electron in naphtho[3,2,1-no]tetraphene is delocalized over the six-ring helical core, but non-uniformly.
  • Monosubstituted derivatives exhibit selective σ-dimer formation due to uneven spin distribution.
  • Tetrasubstituted derivatives, with hindered reactive sites, show suppressed dimerization, enabling characterization.
  • Spectroscopic and DFT results confirm spin delocalization through the chiral backbone.

Conclusions:

  • Naphtho[3,2,1-no]tetraphene serves as a model for studying spin-delocalized helical systems.
  • Nonuniform spin distribution dictates the regioselectivity of σ-dimer formation.
  • Steric hindrance can prevent dimerization, allowing for the isolation and characterization of persistent open-shell helical molecules.