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Related Concept Videos

¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

2.8K
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...
2.8K
Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

1.5K
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,...
1.5K
Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

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

1.6K
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...
1.6K
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

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

1.8K
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...
1.8K
NMR Spectroscopy: Spin–Spin Coupling01:08

NMR Spectroscopy: Spin–Spin Coupling

3.4K
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...
3.4K
Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

1.6K
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...
1.6K

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Setting Limits on Supersymmetry Using Simplified Models
07:46

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Published on: November 15, 2013

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Coupling strength assumption in statistical energy analysis.

T Lafont1,2, N Totaro1, A Le Bot2

  • 1Laboratoire de Tribologie et Dynamique des Systèmes, École Centrale de Lyon, 69134 Écully, France.

Proceedings. Mathematical, Physical, and Engineering Sciences
|May 10, 2017
PubMed
Summary
This summary is machine-generated.

Statistical energy analysis (SEA) coupling power proportionality holds for two oscillators but fails for three subsystems under strong coupling. This can reverse energy flow direction, impacting vibrational analysis.

Keywords:
sound and vibrationstatistical energy analysisweak coupling

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Area of Science:

  • Mechanical Engineering
  • Acoustics
  • Vibrational Analysis

Background:

  • Statistical Energy Analysis (SEA) is a method for predicting vibrational energy flow in complex structures.
  • The hypothesis of weak coupling is fundamental to many SEA formulations.
  • Understanding the limits of SEA is crucial for accurate vibrational energy predictions.

Purpose of the Study:

  • To investigate the validity of the weak coupling hypothesis in Statistical Energy Analysis.
  • To examine the behavior of SEA under strong coupling conditions.
  • To analyze the impact of strong coupling on energy flow and loss factors.

Main Methods:

  • Comparison of reference calculations with SEA calculations for coupled oscillators and plates.
  • Analysis of energy flow and coupling power proportionality in systems with varying coupling strengths.
  • Examination of indirect coupling loss factors and energy flow direction.

Main Results:

  • The main SEA relation, coupling power proportionality, is always valid for two coupled oscillators, regardless of coupling strength.
  • For three subsystems (oscillators or plates), coupling power proportionality fails under strong coupling.
  • Strong coupling results in non-zero indirect coupling loss factors and potential reversal of energy flow.

Conclusions:

  • The weak coupling assumption in SEA is not universally valid, particularly for systems with three or more strongly coupled subsystems.
  • Strong coupling necessitates a re-evaluation of SEA models to account for indirect coupling effects and potential energy flow reversals.
  • Accurate vibrational energy analysis requires careful consideration of coupling strength in SEA applications.