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Related Concept Videos

¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

2.6K
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...
2.6K
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

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

1.6K
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...
1.6K
Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)

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...
1.4K
Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

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

Spin–Spin Coupling Constant: Overview

1.4K
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...
1.4K
NMR Spectroscopy: Spin–Spin Coupling01:08

NMR Spectroscopy: Spin–Spin Coupling

2.9K
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...
2.9K

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Related Experiment Video

Updated: Jan 8, 2026

High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal
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High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal

Published on: October 31, 2019

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Ion-order coupling in nematic liquid crystals.

Rajratan Basu1

  • 1United States Naval Academy, Department of Physics, Soft Matter and Nanomaterials Laboratory, The , Annapolis, Maryland 21402, USA.

Physical Review. E
|December 23, 2025
PubMed
Summary

Ionic impurities in liquid crystals (LC) were quantitatively studied. A new model explains how ions affect dielectric anisotropy and rotational viscosity, validated by experiments with graphene-doped LC.

Area of Science:

  • Soft matter physics
  • Materials science
  • Physical chemistry

Background:

  • Ionic impurities impact nematic liquid crystal (LC) properties, but quantitative understanding is lacking.
  • Existing models do not fully capture the complex interplay between ions and LC material parameters.

Purpose of the Study:

  • To develop and validate a predictive theoretical framework for ion effects in nematic LCs.
  • To quantitatively link ionic screening to macroscopic rheo-optic behavior.

Main Methods:

  • Integrated ionic Coulomb self-energy into the Landau-de Gennes formalism.
  • Developed a model for electrostatic ion drag's effect on rotational viscosity.
  • Experimentally verified models using graphene-doped dual-frequency nematic LC.
  • Conducted dynamic optical switching measurements.

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Measuring Magnetically-Tuned Ferroelectric Polarization in Liquid Crystals

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Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets
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Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets

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Last Updated: Jan 8, 2026

High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal
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High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal

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Measuring Magnetically-Tuned Ferroelectric Polarization in Liquid Crystals
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Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets
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Main Results:

  • The theoretical framework accurately predicts the nonlinear suppression of dielectric anisotropy by free ions.
  • The ion drag model successfully explains the increase in rotational viscosity.
  • Experimental results show strong agreement with theoretical predictions across various dielectric regimes.
  • Optical switching measurements confirm the findings on rotational viscosity.

Conclusions:

  • Established a self-consistent link between microscopic ionic screening and macroscopic rheo-optic behavior in liquid crystals.
  • Advanced the fundamental understanding of ion-related electrostatics in complex fluids.
  • Provided a predictive tool for designing LC materials with tailored properties.