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Related Concept Videos

Radical Reactivity: Intramolecular vs Intermolecular01:33

Radical Reactivity: Intramolecular vs Intermolecular

Radical reactions can occur either intermolecularly or intramolecularly. In an intermolecular radical reaction, a nucleophilic radical adds to an electrophilic alkene or vice versa. In such reactions, the radical and generally the alkene, which is also called the radical trap, are two different molecules. Additionally, for such intermolecular reactions to occur, the radical trap must be active, present in an excess concentration, and the radical starting material must have a weak carbon–halogen...
Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
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Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
Woodward–Hoffmann Selection Rules and Microscopic Reversibility01:34

Woodward–Hoffmann Selection Rules and Microscopic Reversibility

Electrocyclic reactions, cycloadditions, and sigmatropic rearrangements are concerted pericyclic reactions that proceed via a cyclic transition state. These reactions are stereospecific and regioselective. The stereochemistry of the products depends on the symmetry characteristics of the interacting orbitals and the reaction conditions. Accordingly, pericyclic reactions are classified as either symmetry-allowed or symmetry-forbidden. Woodward and Hoffmann presented the selection criteria for...
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ortho–para-Directing Activators: –CH3, –OH, –⁠NH2, –OCH3

All ortho–para directors, excluding halogens, are activating groups. These groups donate electrons to the ring, making the ring carbons electron-rich. Consequently, the reactivity of the aromatic ring towards electrophilic substitution increases. For instance, the nitration of anisole is about 10,000 times faster than the nitration of benzene. The electron-donating effect of the methoxy group in anisole activates the ortho and para positions on the ring and stabilizes the corresponding...

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Direct Imaging of Laser-driven Ultrafast Molecular Rotation
10:52

Direct Imaging of Laser-driven Ultrafast Molecular Rotation

Published on: February 4, 2017

Intramolecular electron arrangement with a rotative trigger.

Shoko Kume1, Kuniharu Nomoto, Tetsuro Kusamoto

  • 1Department of Chemistry, Graduate School of Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. kume@chem.s.u-tokyo.ac.jp

Journal of the American Chemical Society
|September 25, 2009
PubMed
Summary

Electron transfer in a single molecule system is controlled by molecular rotation. This study reveals how ferrocene-tethered copper complexes exhibit synchronized motion and electron migration, switching redox activity with temperature.

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Area of Science:

  • Supramolecular Chemistry
  • Molecular Electronics
  • Coordination Chemistry

Background:

  • Single-molecule systems offer precise control over chemical and physical processes.
  • Electron transfer is fundamental to many biological and chemical systems.
  • Molecular motion can influence electronic properties.

Purpose of the Study:

  • To construct and characterize a single molecule system where electron transfer is triggered by molecular motion.
  • To investigate the interplay between molecular conformation, redox activity, and temperature.
  • To elucidate the mechanism of synchronized motion and electron migration.

Main Methods:

  • X-ray crystallography for structural characterization of isomers.
  • Proton Nuclear Magnetic Resonance ((1)H NMR) spectroscopy to study isomer interconversion.
  • Electrochemical measurements to determine redox potentials.
  • Electron Paramagnetic Resonance (EPR) and UV-Vis absorption spectroscopy to monitor oxidation and spectral changes.

Main Results:

  • A ferrocene-tethered copper complex with two distinct coordination conformations was synthesized.
  • Isomers interconvert via pyrimidine rotation at room temperature, freezing below 233 K.
  • Oxidation state influences isomer stability, causing spontaneous isomerization.
  • Electron transfer identity (copper vs. ferrocene) alternates based on temperature and molecular motion.
  • Synchronized motion and electron migration observed as a one-step spectral conversion.

Conclusions:

  • Molecular rotational motion can effectively trigger and control electron transfer in single-molecule systems.
  • The system demonstrates a temperature-dependent switching of redox centers.
  • This work provides insights into designing molecular devices with tunable electronic properties based on conformational changes.