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Related Concept Videos

π Electron Effects on Chemical Shift: Overview01:27

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An applied magnetic field causes loosely bound π-electrons in organic molecules to circulate, producing a local or induced diamagnetic field over a large spatial volume. As the molecules tumble in solution, the field generated by π-electrons in spherical substituents results in a zero net field. However, the net field generated by π-electrons in non-spherical substituents is not zero. The effect of this induced field depends on the orientation of the molecule with respect to B0,...
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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,...
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¹H NMR: Long-Range Coupling01:27

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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.
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π Molecular Orbitals of 1,3-Butadiene01:24

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Conjugated dienes have lower heats of hydrogenation than cumulated and isolated dienes, making them more stable. The enhanced stabilization of conjugated systems can be understood from their π molecular orbitals.
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At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
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¹H NMR: Complex Splitting01:13

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A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
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CH-π Interactions Elucidated at the Single-Molecule Level.

Qianyuan Ren1,2, Wenying Hao2,3, Lixia Wang4

  • 1College of Food and Bioengineering, Xihua University, Chengdu 610039, China.

Journal of the American Chemical Society
|August 29, 2025
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Summary
This summary is machine-generated.

This study quantifies CH-π interactions using a protein nanopore system. Deuterium forms weaker CD-π interactions than protic CH-π interactions, resolving a long-standing scientific debate.

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Area of Science:

  • Biophysics
  • Chemical Physics
  • Molecular Interactions

Background:

  • CH-π interactions are crucial molecular forces in biological and chemical systems.
  • Experimentally measuring weak CH-π interactions is challenging due to stronger concurrent noncovalent forces.

Purpose of the Study:

  • To accurately compare the strength of CH-π interactions between phenylalanine derivatives and aliphatic amino acids.
  • To resolve the debate on the deuterium isotope effect in CH-π interactions.

Main Methods:

  • Utilized a refined protein nanopore system for molecular exchange processes.
  • Quantitatively compared binding strengths to determine interaction forces.

Main Results:

  • CH-π interactions are dominated by dispersive attraction.
  • More acidic C-H bonds lead to stronger CH-π interactions.
  • Confirmed that deuterium forms weaker CD-π interactions compared to CH-π interactions.

Conclusions:

  • The study provides a robust method for measuring weak CH-π interactions.
  • Resolved the deuterium isotope effect, showing CD-π interactions are weaker than CH-π interactions.