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Related Concept Videos

¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

2.9K
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...
2.9K
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

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

2.0K
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...
2.0K
Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

1.6K
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,...
1.6K
¹H NMR: Pople Notation01:09

¹H NMR: Pople Notation

2.9K
The Pople nomenclature system classifies spin systems based on the difference between their chemical shifts. Coupled spins are denoted by capital letters with subscripts indicating the number of equivalent nuclei. When the coupled nuclei have well-separated chemical shifts, they are assigned letters that are far apart in the alphabet, such as A and X. When the difference in chemical shifts is small, coupled nuclei are named using adjacent letters of the alphabet (AB, MN, or XY).
A proton...
2.9K
Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule01:10

Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule

3.2K
In the AX proton spin system, proton A can sense the two spin states of a coupled proton X, resulting in a doublet NMR signal with two peaks of equal (1:1) intensity. When proton A is coupled to two equivalent protons (AX2 spin system), the spin states of each X can be aligned with or against the external field, creating three possible scenarios. This results in a 1:2:1  triplet signal, where the central peak corresponds to the chemical shift of A and is twice as large or intense as the...
3.2K
Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

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

1.7K
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...
1.7K

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Updated: Apr 11, 2026

Construction and Systematical Symmetric Studies of a Series of Supramolecular Clusters with Binary or Ternary Ammonium Triphenylacetates
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Pair extended coupled cluster doubles.

Thomas M Henderson1, Ireneusz W Bulik1, Gustavo E Scuseria1

  • 1Department of Chemistry, Rice University, Houston, Texas 77005-1892, USA.

The Journal of Chemical Physics
|June 8, 2015
PubMed
Summary
This summary is machine-generated.

Pair extended coupled cluster doubles (pECCD) offers accurate descriptions of strongly correlated systems at low computational cost. This method reproduces doubly occupied configuration interaction (DOCI) energies and wave functions, outperforming pCCD for attractive interactions.

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Area of Science:

  • Computational chemistry
  • Quantum chemistry
  • Strongly correlated systems

Background:

  • Accurate computational methods for strongly correlated systems are crucial but often computationally expensive.
  • Doubly occupied configuration interaction (DOCI) provides accurate results but has combinatorial costs.
  • Pair coupled cluster doubles (pCCD) offers a computationally cheaper alternative, closely matching DOCI energies.

Purpose of the Study:

  • Introduce the pair extended coupled cluster doubles (pECCD) method.
  • Evaluate pECCD's accuracy in describing strongly correlated systems.
  • Compare pECCD's performance against pCCD and DOCI.

Main Methods:

  • Development of the pECCD computational method.
  • Energetic and wave function comparisons between pECCD, pCCD, and DOCI.
  • Assessment of performance for attractive interaction scenarios.

Main Results:

  • pECCD achieves mean-field computational cost, similar to pCCD.
  • pECCD accurately reproduces DOCI energies.
  • pECCD demonstrates high accuracy in reproducing DOCI wave functions, surpassing pCCD.
  • pECCD provides meaningful results for attractive interactions where pCCD fails.

Conclusions:

  • pECCD is an accurate and efficient method for strongly correlated systems.
  • pECCD offers a significant improvement over pCCD in wave function accuracy and applicability.
  • The development of pECCD advances computational chemistry for complex electronic systems.