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

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

1.9K
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...
1.9K
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
NMR Spectroscopy: Spin–Spin Coupling01:08

NMR Spectroscopy: Spin–Spin Coupling

3.6K
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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An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids
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Dynamic Coupling at the Ångström Scale.

Krishna Kanti Dey1, Frances Ying Pong1, Jens Breffke1

  • 1Department of Chemistry, The Pennsylvania State University, University Park, PA, 16802, USA.

Angewandte Chemie (International Ed. in English)
|December 5, 2015
PubMed
Summary
This summary is machine-generated.

Active particles drive momentum transfer and enhance diffusion even at the molecular scale, challenging previous assumptions about viscosity dominance. This phenomenon impacts advection and mixing at the Ångström scale.

Keywords:
NMR spectroscopycatalysisdiffusionorganometallic compoundsself-propulsion

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Area of Science:

  • Physical Chemistry
  • Chemical Physics
  • Soft Matter Physics

Background:

  • Momentum transfer from active particles is known in microscale systems.
  • It was previously assumed unlikely at molecular scales due to high viscosity.
  • The role of active particles in molecular-scale transport was poorly understood.

Purpose of the Study:

  • To investigate momentum transfer and diffusion enhancement at the Ångström scale.
  • To determine if active particle behavior at molecular scales mirrors microscale systems.
  • To explore the impact of active catalysts and enzymes on passive tracer motion.

Main Methods:

  • Diffusion Nuclear Magnetic Resonance (NMR) spectroscopy was employed.
  • The motion of passive tracers (tetramethylsilane, benzene) in an active Grubbs catalyst solution was studied.
  • Enzyme urease in aqueous solution was also investigated.

Main Results:

  • Significant enhancements in diffusion were observed for both tracers and the active catalyst.
  • Diffusion enhancement correlated with the reaction rate of the active particles.
  • Similar diffusion enhancements were observed for the enzyme urease.
  • Molecular-scale momentum transfer was found to resemble microscale systems.
  • The observed momentum transfer was independent of the specific swimming mechanism.

Conclusions:

  • Active particles can induce momentum transfer and enhance diffusion at the Ångström scale.
  • This molecular-scale phenomenon is analogous to that observed in microscale systems.
  • The findings provide new insights into active particle-driven advection and mixing at the molecular level.