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Related Concept Videos

Conformations of Cyclohexane02:11

Conformations of Cyclohexane

Cyclohexane does not exist in a planar form due to the high angle and torsional strain it would experience in the planar structure. Instead, it adopts non-planar chair and boat conformations.
The chair form is the most stable and derives its name from its resemblance to the “easy chair.” In the chair conformation, two carbon atoms are arranged out-of-plane — one above and one below, minimizing the torsional strain. In the chair form, the bond angle is very close to the ideal tetrahedral value,...
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 Anions: Structural Overview01:18

Aromatic Hydrocarbon Anions: Structural Overview

Neutral hydrocarbons like cyclopentadiene with an odd number of carbon atoms and one intervening CH2 group in the ring are not aromatic. Cyclopentadiene with 4 π electrons does not satisfy the 4n + 2 π electron rule. Additionally, the intervening CH2 group is sp3 hybridized and lacks a vacant p orbital, thereby interrupting the overlap of p orbitals in a continuous manner and preventing the delocalization of π electrons throughout the ring.
Due to the absence of continuous overlap of p...
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.
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...
Radicals: Electronic Structure and Geometry01:07

Radicals: Electronic Structure and Geometry

This lesson delves into the geometry of a radical, which is influenced by the electronic structure of the molecule. The principle is similar to that of a lone pair, where the unpaired electron influences the geometry at the radical center.
Accordingly, the structure of a trivalent radical lies between the geometries of carbocations and carbanions. An sp2-hybridized carbocation is trigonal planar, while an sp3-hybridized carbanion is trigonal pyramidal. Here, the difference in geometry is...

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Self-assembling Morphologies Obtained from Helical Polycarbodiimide Copolymers and Their Triazole Derivatives
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Degenerate [2]rotaxanes with electrostatic barriers.

Hao Li1, Yan-Li Zhao, Albert C Fahrenbach

  • 1Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, USA.

Organic & Biomolecular Chemistry
|February 24, 2011
PubMed
Summary

Researchers developed new [2]rotaxanes with bispyridinium units and cyclobis(paraquat-p-phenylene) tetracationic rings. These molecules exhibit controlled ring shuttling between recognition sites due to electrostatic interactions and redox activity.

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Area of Science:

  • Supramolecular Chemistry
  • Materials Science
  • Organic Synthesis

Background:

  • Rotaxanes are mechanically interlocked molecular architectures with potential applications in molecular machines.
  • Cyclobis(paraquat-p-phenylene) tetracationic (CBPQT(4+)) rings are widely used macrocycles in rotaxane construction.
  • Bispyridinium units offer tunable electronic properties for molecular recognition.

Purpose of the Study:

  • To synthesize novel [2]rotaxanes incorporating bispyridinium derivatives and 1,5-dioxynaphthalene (DNP) units.
  • To investigate the influence of π-electron-deficient bispyridinium units on the shuttling dynamics of the CBPQT(4+) ring.
  • To explore redox-controlled switching of the rotaxane system.

Main Methods:

  • Synthetic preparation of [2]rotaxanes (1-5·6PF(6)) with specific dumbbell components.
  • Variable-temperature (1)H NMR spectroscopy to study ring shuttling dynamics.
  • Electrochemical experiments to probe redox states and recognition sites.

Main Results:

  • Successful synthesis of [2]rotaxanes featuring bispyridinium and DNP units.
  • Observed slow shuttling of the CBPQT(4+) ring between DNP sites due to electrostatic repulsion from bispyridinium units.
  • Identified the one-electron reduced bipyridinium radical cation as an additional recognition site for the reduced CBPQT(2(˙+)) ring.
  • Demonstrated redox-controlled shuttling along DNP and reduced bipyridinium sites.

Conclusions:

  • The incorporation of bispyridinium units effectively modulates the shuttling behavior of CBPQT(4+)-based rotaxanes.
  • Rotaxanes can be designed with multiple, switchable recognition sites for advanced molecular machinery.
  • Redox control offers a viable strategy for manipulating molecular motion in synthetic systems.