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Related Concept Videos

¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

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 π orbitals.
Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

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

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

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

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...
π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds01:14

π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds

In aromatic compounds, such as benzene, the circulation of (4n + 2) π-electrons sets up a diamagnetic or diatropic ring current around the perimeter of the molecule. This current induces a magnetic field that opposes the external field inside the ring and reinforces it on the outside. The protons in benzene are deshielded and exhibit high chemical shifts in the range 6.5–8.5 ppm. The shielding effect at the center of the ring is evident in complex aromatic molecules, such as annulenes. In...
Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

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,...
π Electron Effects on Chemical Shift: Overview01:27

π Electron Effects on Chemical Shift: Overview

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, resulting in...

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Using Cyclic Voltammetry, UV-Vis-NIR, and EPR Spectroelectrochemistry to Analyze Organic Compounds
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Modulation of electronic couplings within Ru2-polyyne frameworks.

Bin Xi1, Isiah P-C Liu, Guo-Lin Xu

  • 1Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States.

Journal of the American Chemical Society
|August 23, 2011
PubMed
Summary
This summary is machine-generated.

Ruthenium dimers bridged by hexatriyne were synthesized and reacted with TCNE or cobalt complexes. Electronic coupling between ruthenium centers was modulated by these reactions, impacting their mixed-valence properties.

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Area of Science:

  • Inorganic Chemistry
  • Materials Science
  • Electrochemistry

Background:

  • Ruthenium-based dimers with bridging ligands are of interest for their electronic and photophysical properties.
  • Understanding electronic communication in mixed-valence systems is crucial for developing advanced materials.

Purpose of the Study:

  • To synthesize and characterize novel ruthenium dimers bridged by 1,3,5-hexatriyn-diyl.
  • To investigate the effect of tetracyanoethene (TCNE) and cobalt complex addition on the electronic coupling between the ruthenium centers.

Main Methods:

  • Synthesis of ruthenium dimers ([Ru(2)(Xap)(4)](2)(μ-C(6)))
  • Reactions with tetracyanoethene (TCNE) and cobalt complexes (Co(2)(dppm)(CO)(6))
  • Voltammetric and spectroelectrochemical studies
  • X-ray diffraction analysis
  • Spin-unrestricted DFT calculations

Main Results:

  • Successful synthesis of ruthenium dimers bridged by 1,3,5-hexatriyn-diyl.
  • Formation of cyclo-addition/insertion products with TCNE and η(2)-Co(2) adducts with cobalt complexes.
  • Ruthenium dimers in the parent compound exhibit significant electronic coupling (Robin-Day class II/III).
  • Electronic coupling is weakened in cobalt adducts and completely removed upon TCNE insertion.

Conclusions:

  • The electronic coupling between ruthenium centers in these dimers can be effectively tuned by chemical modification.
  • TCNE insertion significantly disrupts electronic communication, while cobalt complexation causes a moderate attenuation.
  • Structural and computational studies support the observed electronic coupling behavior.