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

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...

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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.
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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: 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.
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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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Related Experiment Video

Updated: Mar 15, 2026

Nanomanipulation of Single RNA Molecules by Optical Tweezers

Nanomanipulation of Single RNA Molecules by Optical Tweezers

Published on: August 20, 2014

s± pairing near a Lifshitz transition.

Vivek Mishra¹, Douglas J Scalapino², Thomas A Maier³

¹Joint Institute of Computational Sciences, University of Tennessee, Knoxville, TN-37996, USA.

Scientific Reports

|August 27, 2016

Summary

Spin-fluctuation theories explain robust superconductivity near Lifshitz points in iron-based superconductors. This study models a bilayer Hubbard model, finding s± pairing and a transition temperature peaking beyond the Lifshitz point.

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Nanomanipulation of Single RNA Molecules by Optical Tweezers

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Area of Science:

Condensed Matter Physics
Materials Science

Background:

Iron-based superconductors exhibit robust superconductivity near Lifshitz points.
Spin density wave instabilities are suppressed as hole bands drop below the Fermi energy.
This phenomenon challenges existing spin-fluctuation theories.

Purpose of the Study:

To investigate spin-fluctuation pairing mechanisms in iron-based superconductors.
To analyze the behavior of a bilayer Hubbard model undergoing a Lifshitz transition.
To reconcile theoretical models with experimental observations of superconductivity.

Main Methods:

Theoretical modeling using a bilayer Hubbard model.
Analysis of Lifshitz transitions and their impact on electronic band structure.
Investigation of spin-fluctuation pairing and gap function properties.

Main Results:

The study confirms s± pairing in the investigated model.
A peak in the superconducting transition temperature is observed beyond the Lifshitz point.
The gap function exhibits consistent magnitude but opposite sign across different bands.

Conclusions:

Spin-fluctuation pairing provides a viable mechanism for superconductivity in this context.
The Lifshitz transition plays a crucial role in modulating superconducting properties.
The findings offer insights into the complex interplay of electronic correlations and superconductivity in iron-based materials.