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Related Concept Videos

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

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

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

Spin–Spin Coupling Constant: Overview

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 have a...
Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

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

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

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...
¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

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 π orbitals.
Magnetic Field Due To A Thin Straight Wire01:27

Magnetic Field Due To A Thin Straight Wire

Consider an infinitely long straight wire carrying a current I. The magnetic field at point P at a distance a from the origin can be calculated using the Biot-Savart law.

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Related Experiment Video

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Magnetic Tweezers for the Measurement of Twist and Torque
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Published on: May 19, 2014

Ultrahigh Casimir interaction torque in nanowire systems.

Tiago A Morgado1, Stanislav I Maslovski, Mário G Silveirinha

  • 1University of Coimbra, Department of Electrical Engineering–Instituto de Telecomunicações, 3030-290 Coimbra, Portugal.

Optics Express
|June 22, 2013
PubMed
Summary

Researchers studied Casimir torque from quantum fluctuations in metallic nanorod arrays. The dense nanorod system channels fluctuations, significantly boosting torque compared to other methods.

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Last Updated: May 10, 2026

Magnetic Tweezers for the Measurement of Twist and Torque
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Published on: May 19, 2014

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Ultrahigh Density Array of Vertically Aligned Small-molecular Organic Nanowires on Arbitrary Substrates

Published on: June 18, 2013

Area of Science:

  • Condensed matter physics
  • Quantum optics
  • Nanotechnology

Background:

  • The Casimir effect describes a physical force arising from quantum field fluctuations.
  • Torque, a rotational force, can also arise from these quantum fluctuations.
  • Controlling quantum fluctuations is key to manipulating Casimir forces.

Purpose of the Study:

  • To investigate the Casimir torque in a system of metallic nanorods.
  • To explore the potential for enhancing Casimir torque using nanostructured materials.
  • To understand the role of photonic states in mediating Casimir interactions.

Main Methods:

  • Theoretical modeling of quantum electromagnetic fluctuations.
  • Simulation of a dense array of metallic nanorods in dielectric fluids.
  • Analysis of the interaction between two interfaces within the nanorod system.

Main Results:

  • Demonstrated channeling of quantum fluctuations due to the high density of photonic states.
  • Observed a significant boost in Casimir torque, several orders of magnitude higher than in other systems.
  • Identified the nanorod array structure as crucial for torque enhancement.

Conclusions:

  • Dense metallic nanorod arrays can effectively channel quantum fluctuations.
  • This channeling leads to a substantial enhancement of Casimir torque.
  • The findings offer new possibilities for manipulating quantum forces at the nanoscale.