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Related Concept Videos

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.
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.
Selection Rules: Photochemical Activation
Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group with both...
[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement01:21

[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement

The Cope rearrangement is classified as a [3,3] sigmatropic shift in 1,5-dienes, leading to a more stable, isomeric 1,5-diene. The reaction involves a concerted movement of six electrons, four from two π bonds and two from a σ bond, via an energetically favorable chair-like transition state.
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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Design, Synthesis, and Photochemical Properties of Clickable Caged Compounds
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Toward electrochemically controllable tristable three-station [2]catenanes.

Taichi Ikeda1, Sourav Saha, Ivan Aprahamian

  • 1The California NanoSystems Institute, USA.

Chemistry, an Asian Journal
|April 19, 2007
PubMed
Summary

Researchers developed novel electrochemical, color-switchable dye compounds using two three-station [2]catenanes. These molecular machines exhibit distinct bistable and quasi-tristable behaviors, paving the way for advanced materials.

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Published on: October 18, 2018

Area of Science:

  • Supramolecular Chemistry
  • Materials Science
  • Electrochemistry

Background:

  • Development of electrochemical, color-switchable dye compounds is a key area for advanced materials.
  • Catenanes, mechanically interlocked molecules, offer unique platforms for molecular machines.
  • Designing multi-station catenanes is crucial for complex molecular functionalities.

Purpose of the Study:

  • To design, synthesize, and characterize novel three-station [2]catenanes for potential RGB dye applications.
  • To investigate the molecular recognition and self-assembly properties of these catenanes with a cyclophane.
  • To evaluate the electrochemical and electromechanical behavior of the synthesized catenanes.

Main Methods:

  • Synthesis and full characterization of two three-station [2]catenanes using mass spectrometry and 1H NMR spectroscopy.
  • Synthesis of model compounds to determine relative station occupancies.
  • Isothermal titration calorimetry (ITC) to quantify binding thermodynamics.
  • Cyclic voltammetry (CV), differential pulse voltammetry (DPV), and spectroelectrochemistry (SEC) for electrochemical analysis.

Main Results:

  • Two novel three-station [2]catenanes composed of macrocyclic polyethers with pi-electron-rich stations were successfully synthesized and characterized.
  • Thermodynamic parameters from ITC revealed the relative ground-state populations of station occupancy by the cyclophane.
  • Electrochemical analysis showed the first catenane functions as a bistable system, while the second exhibits quasi-tristable behavior.

Conclusions:

  • The synthesized three-station [2]catenanes demonstrate tunable electrochemical and electromechanical properties.
  • The observed bistable and quasi-tristable behaviors are promising for developing electrochemical, color-switchable RGB dye compounds.
  • This work advances the design principles for complex molecular machines with controllable functions.