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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.
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...
Chair Conformation of Cyclohexane02:02

Chair Conformation of Cyclohexane

The chair conformation is the most stable form of cyclohexane due to the absence of angle and torsional strain. The absence of angle strain is a result of cyclohexane’s bond angle being very close to the ideal tetrahedral bond angle of 109.5° in its chair conformer. Similarly, the torsional strain is also absent owing to the perfectly staggered arrangement of bonds.
The hydrogen atoms linked to carbons are arranged in two different axial and equatorial orientations to achieve this staggered...
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...
Conformations of Cycloalkanes02:29

Conformations of Cycloalkanes

Adolf von Baeyer attempted to explain the instabilities of small and large cycloalkane rings using the concept of angle strain — the strain caused by the deviation of bond angles from the ideal 109.5° tetrahedral value for sp3  hybridized carbons. However, while cyclopropane and cyclobutane are strained, as expected from their highly compressed bond angles, cyclopentane is more strained than predicted, and cyclohexane is virtually strain-free. Hence, Baeyer’s theory that was based on the...

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Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
10:44

Isolating Free Carbenes, their Mixed Dimers and Organic Radicals

Published on: April 19, 2019

Beta-substituted terthiophene [2]rotaxanes.

Taichi Ikeda1, Masayoshi Higuchi, Dirk G Kurth

  • 1Functional Modules Group, Organic Nanomaterials Center, National Institute for Materials Science, 1-1 Namiki Tsukuba Ibaraki 305-0044, Japan. IKEDA.Taichi@nims.go.jp

Chemistry (Weinheim an Der Bergstrasse, Germany)
|March 25, 2009
PubMed
Summary
This summary is machine-generated.

New beta-substituted terthiophene [2]rotaxanes were synthesized. The interlocked cyclophane suppressed polymerization, showing potential for creating novel polythiophene polyrotaxanes.

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Photogeneration of N-Heterocyclic Carbenes: Application in Photoinduced Ring-Opening Metathesis Polymerization
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Depolymerizable Olefinic Polymers Based on Fused-Ring Cyclooctene Monomers
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Depolymerizable Olefinic Polymers Based on Fused-Ring Cyclooctene Monomers

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Area of Science:

  • Supramolecular Chemistry
  • Materials Science
  • Organic Chemistry

Background:

  • Rotaxanes are mechanically interlocked molecules with potential applications in molecular machines and materials.
  • Terthiophenes are conjugated polymers with interesting electronic and optical properties.
  • Cyclobis(paraquat-p-phenylene) (CBPQT(4+)) is a well-established electron-deficient macrocycle host.

Purpose of the Study:

  • To synthesize and characterize novel beta-substituted terthiophene [2]rotaxanes.
  • To investigate the influence of the CBPQT(4+) host on the properties of terthiophene guests.
  • To explore the potential of these rotaxanes as precursors for polythiophene polyrotaxanes.

Main Methods:

  • Synthesis of two beta-substituted terthiophene [2]rotaxanes (3 T-beta-Rx and 3 TBr-beta-Rx) using CBPQT(4+).
  • Binding constant determination.
  • UV/Vis absorption spectroscopy to detect charge-transfer (CT) bands.
  • Fluorescence spectroscopy to study quenching effects.
  • Electrochemical measurements (cyclic voltammetry) to assess polymerizability and redox properties.

Main Results:

  • Synthesized beta-substituted terthiophene [2]rotaxanes with smaller binding constants than alpha-substituted analogues.
  • Confirmed charge-transfer (CT) bands and strong fluorescence quenching in the rotaxanes.
  • Demonstrated that the [2]rotaxane 3 T-beta-Rx is not electrochemically polymerizable due to CBPQT(4+) interference.
  • Observed shifts and splitting in the reduction potentials of CBPQT(4+) within the rotaxane structure, similar to highly-constrained systems.

Conclusions:

  • Beta-substituted terthiophene [2]rotaxanes were successfully synthesized and characterized.
  • The interlocked CBPQT(4+) macrocycle significantly hinders the electrochemical polymerization of the terthiophene unit.
  • These beta-substituted terthiophene [2]rotaxanes are key intermediates for the development of polythiophene polyrotaxanes.