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

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

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

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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.
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Spin–Spin Coupling Constant: Overview01:08

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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...
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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.
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...
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IR Spectroscopy: Hooke's Law Approximation of Molecular Vibration01:16

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A covalently bonded heteronuclear diatomic molecule can be modeled as two vibrating masses connected by a spring. The vibrational frequency of the bond can be expressed using an equation derived from Hooke's law, which describes how the force applied to stretch or compress a spring is proportional to the displacement of the spring. In this case, the atoms behave like masses, and the bond acts like a spring.
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Tuning Patchy Bonds Induced by Critical Casimir Forces.

Truc A Nguyen1,2, Arthur Newton3, Daniela J Kraft4

  • 1Institute of Physics, University of Amsterdam, 1098 XH Amsterdam, The Netherlands. ngtranh@gmail.com.

Materials (Basel, Switzerland)
|November 4, 2017
PubMed
Summary
This summary is machine-generated.

Controlling patchy particle interactions by adjusting patch width influences colloidal structure formation. Narrower patches promote chain-like assemblies due to geometric exclusion effects.

Keywords:
colloidal assemblycritical Casimir effectpatchy colloid

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Area of Science:

  • Colloid science
  • Materials science
  • Soft matter physics

Background:

  • Controlling interactions in patchy colloidal particles is key for assembling complex structures.
  • Critical Casimir forces offer a tunable method for mediating these interactions.

Purpose of the Study:

  • To investigate how patch width affects the assembly of patchy colloidal particles.
  • To understand the role of geometric exclusion in dictating bonding morphology.

Main Methods:

  • Synthesis of hydrophobic dumbbell particles with tunable hydrophilic polymer shells.
  • Assembly in near-critical binary solvents to control interaction range via temperature.
  • Computer simulations using effective critical Casimir potentials.

Main Results:

  • Decreasing the patch-to-shell area ratio shifted bonding morphology towards single-bonded configurations.
  • Chain-like structures were observed as a result of altered bonding.
  • Simulations confirmed geometric exclusion by hydrophilic shells as the cause.

Conclusions:

  • Patch width is a critical parameter for controlling colloidal assembly.
  • Engineering particle building blocks allows for rational design of colloidal superstructures.
  • Geometric exclusion effects are significant in patchy particle interactions.