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NMR Spectroscopy: Spin–Spin Coupling

NMR Spectroscopy: Spin–Spin Coupling

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...

Spin–Spin Coupling: One-Bond Coupling

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)

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...

Chirality in Nature

Chirality in Nature

Chirality is the most intriguing yet essential facet of nature, governing life’s biochemical processes and precision. It can be observed from a snail shell pattern in a macroscopic world to an amino acid, the minutest building block of life. Most of the snails around the world have right-coiled shells because of the intrinsic chirality in their genes. All the amino acids present in the human body exist in an enantiomerically pure state, except for glycine - the sole achiral amino acid.

Thermal Electrocyclic Reactions: Stereochemistry

Thermal Electrocyclic Reactions: Stereochemistry

The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.

Photochemical Electrocyclic Reactions: Stereochemistry

Photochemical Electrocyclic Reactions: Stereochemistry

The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation

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Updated: Nov 19, 2025

Coulomb Explosion Imaging as a Tool to Distinguish Between Stereoisomers

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Published on: August 18, 2017

Chirality-Induced Spin Coherence in Electron Transfer Reactions.

¹Department of Chemistry, University of Oxford, Physical and Theoretical Chemistry Laboratory, South Parks Road, Oxford OX1 3QZ, U.K.

The Journal of Physical Chemistry Letters

|January 29, 2021

Summary

Chirality influences electron transfer in chiral molecules, generating quantum coherence instead of spin polarization. This chirality-induced spin coherence can be detected using electron spin echo experiments in radical pairs.

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Last Updated: Nov 19, 2025

Coulomb Explosion Imaging as a Tool to Distinguish Between Stereoisomers

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Published on: August 18, 2017

Experimental Methods for Spin- and Angle-Resolved Photoemission Spectroscopy Combined with Polarization-Variable Laser

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Published on: June 28, 2018

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Published on: November 12, 2016

Area of Science:

Quantum Chemistry
Spin Physics
Molecular Chirality

Background:

Chirality-induced spin selectivity (CISS) effect observed in electrode-molecule electron transfer.
Investigating spin effects in simpler molecular charge transfer reactions.

Purpose of the Study:

Explore electron transfer's effect on spins in chiral single radicals and radical pairs.
Determine if chirality-induced spin coherence can be generated.

Main Methods:

Application of Nakajima-Zwanzig theory.
Theoretical investigation of electron transfer in chiral radical systems.

Main Results:

Chirality and spin-orbit coupling do not induce spin polarization in these systems.
Electron transfer generates quantum coherence between spin states (chirality-induced spin coherence).

Conclusions:

Chirality-induced spin coherence is a novel phenomenon in molecular charge transfer.
Out-of-phase electron spin echo envelope modulation (ESEEM) can detect this effect in oriented radical pairs.