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Related Concept Videos

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: 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...
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: 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,...
NMR Spectroscopy: Spin–Spin Coupling01:08

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 in...
¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...

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Spin-orbit coupling calculations with the two-component normalized elimination of the small component method.

Michael Filatov1, Wenli Zou, Dieter Cremer

  • 1Department of Chemistry, Southern Methodist University, Dallas, Texas 75275-0314, USA.

The Journal of Chemical Physics
|July 5, 2013
PubMed
Summary

A new two-component Normalized Elimination of the Small Component (2cNESC) algorithm accurately calculates spin-orbit splittings in heavy atoms and molecules. This Dirac-exact method shows improved accuracy for two-electron spin-orbit interactions compared to other methods.

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Area of Science:

  • Quantum Chemistry
  • Relativistic Effects in Atoms and Molecules
  • Computational Physics

Background:

  • Spin-orbit (SO) interactions are crucial for understanding electronic structures of heavy elements.
  • Accurate calculation of SO splittings is computationally demanding.
  • Existing methods often involve approximations for two-electron SO interactions.

Purpose of the Study:

  • To present and validate a new algorithm, the two-component Normalized Elimination of the Small Component (2cNESC) method.
  • To accurately calculate spin-orbit splittings in heavy atoms and molecules.
  • To assess the performance of 2cNESC against established methods.

Main Methods:

  • The study employs the Dirac-exact 2cNESC method.
  • It utilizes an exact two-component one-electron Hamiltonian.
  • Two-electron SO interactions are modeled using a screened nucleus potential with effective nuclear charges.

Main Results:

  • The 2cNESC method achieves accurate Dirac SO splittings for one-electron systems.
  • For many-electron systems, it provides accurate spinor energy splittings.
  • Deviations from Dirac-Fock-Coulomb values are significantly smaller than with other methods.

Conclusions:

  • The 2cNESC method is a reliable and accurate approach for calculating SO splittings.
  • It offers improved accuracy for two-electron SO interactions.
  • The method's trends in spinor energies and SO splittings are consistent with chemical principles for hydrogen halides and mercury dihalides.