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Related Concept Videos

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

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...
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,...
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...
P-N junction01:11

P-N junction

A p-n junction is formed when p-type and n-type semiconductor materials are joined together. At the interface of the p-n junction, holes from the p-side and electrons from the n-side begin to diffuse into the opposite sides due to the concentration gradient. This diffusion of carriers leads to a region around the junction where there are no free charge carriers, known as the depletion region. The charge density within the depletion region for the n-side and p-side can be described by 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...
Metal-Semiconductor Junctions01:24

Metal-Semiconductor Junctions

The contact of metal and semiconductor can lead to the formation of a junction with either Schottky or Ohmic behavior.
Schottky Barriers
Schottky barriers arise when a metal with a work function (Φm) contacts a semiconductor with a different work function (Φs). Initially, electrons transfer until the Fermi levels of the metal and semiconductor align at equilibrium. For instance, if Φm > Φs, the semiconductor Fermi level is higher than the metal's before contact. The semiconductor's...

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Updated: Jun 20, 2026

Single-Molecule F&ouml;rster Resonance Energy Transfer Methods for Real-Time Investigation of the Holliday Junction Resolution by GEN1
11:27

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Published on: September 18, 2019

Frustrated rotations in single-molecule junctions.

Young S Park1, Jonathan R Widawsky, Maria Kamenetska

  • 1Department of Chemistry, Columbia University, New York, New York, USA.

Journal of the American Chemical Society
|September 3, 2009
PubMed
Summary
This summary is machine-generated.

Molecular orientation of gold-chalcogen bonds influences electron transport in conjugated molecules. Greater overlap between gold electrodes, chalcogen lone pairs, and aromatic pi systems enhances molecular junction conductivity.

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Area of Science:

  • Molecular electronics
  • Organic chemistry
  • Surface science

Background:

  • Understanding charge transport in molecular junctions is crucial for developing novel electronic devices.
  • The interface between electrodes and organic molecules significantly impacts device performance.

Purpose of the Study:

  • To investigate how the orientation of gold-chalcogen bonds affects electron transport through conjugated molecules.
  • To elucidate the role of chalcogen lone pairs and aromatic pi systems in molecular conductance.

Main Methods:

  • Conductance measurements of specifically designed molecular junctions.
  • Comparison of conductance between different molecular architectures (e.g., 1,4-bis(methylthio)benzene vs. tetrahydrobenzodithiophene).

Main Results:

  • The orientation of gold-sulfur (Au-S) and gold-selenium (Au-Se) bonds relative to the aromatic pi system explicitly controls electron transport.
  • Conduction pathways involve the chalcogen p lone pairs, connecting gold electrodes to the aromatic pi system.
  • Increased overlap between these components leads to higher conductivity.

Conclusions:

  • Molecular orientation at electrode-molecule interfaces is a key factor in controlling charge transport.
  • Chalcogen lone pair interactions with aromatic systems are critical for efficient electron transport in molecular junctions.
  • This work provides fundamental insights for designing high-performance molecular electronic devices.