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Related Concept Videos

Aromatic Hydrocarbon Anions: Structural Overview01:18

Aromatic Hydrocarbon Anions: Structural Overview

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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...
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Conformations of Ethane and Propane02:18

Conformations of Ethane and Propane

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In an organic molecule, free rotation about the carbon-carbon single bond results in energetically different conformers of the molecule. Due to this rotation, called the internal rotation, ethane has two major conformations — staggered and eclipsed.
Staggered conformation is a low energy and more stable conformation with the C-H bonds on the front carbon placed at 60°dihedral angles relative to the C-H bonds on the back carbon, leading to a reduced torsional strain. In staggered...
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Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

2.9K
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...
2.9K
Conformations of Butane02:20

Conformations of Butane

14.4K
Unlike ethane and propane that have only two major conformations, butane has more than two conformers. The staggered form of butane in which the bulky methyl groups on the two carbons are placed on opposite sides, that is, at a dihedral angle of 180°, is the lowest energy, most stable form — called the anti conformer. This conformation is stabilized due to the absence of steric repulsion between the largely spaced out methyl groups. The other two staggered conformations are...
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Chair Conformation of Cyclohexane02:02

Chair Conformation of Cyclohexane

14.8K
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...
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¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

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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...
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Microfluidic-based Synthesis of Covalent Organic Frameworks COFs: A Tool for Continuous Production of COF Fibers and Direct Printing on a Surface
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Covalent organic framework atropisomers with multiple gas-triggered structural flexibilities.

Chengjun Kang1, Zhaoqiang Zhang1, Shinpei Kusaka2

  • 1Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore, Singapore.

Nature Materials
|April 10, 2023
PubMed
Summary
This summary is machine-generated.

Researchers discovered atropisomerism in covalent organic frameworks (COFs), creating flexible COF-320-A crystals. This breakthrough enables novel gas sorption behaviors and advances soft porous crystal applications.

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Area of Science:

  • Materials Science
  • Crystallography
  • Supramolecular Chemistry

Background:

  • Covalent organic frameworks (COFs) are crystalline porous polymers with application potential but often lack gas-triggered flexibility.
  • Atropisomerism, a form of isomerism arising from hindered rotation around a single bond, has been known since 1922 but rarely observed in infinite crystalline frameworks.

Purpose of the Study:

  • To investigate and report the experimental discovery of atropisomerism in single crystals of covalent organic frameworks (COFs).
  • To characterize the structural and gas sorption properties of novel COF atropisomers and compare them to existing materials.

Main Methods:

  • Synthesis of COF atropisomers (COF-320 and COF-320-A) with identical chemical and interpenetrated structures but differing spatial arrangements.
  • Single-crystal structure determination using continuous rotation electron diffraction.
  • In situ powder X-ray diffraction to study gas sorption behaviors.
  • Analysis of gas adsorption isotherms at various temperatures.

Main Results:

  • Atropisomerism was successfully achieved in COF single crystals, yielding COF-320 and COF-320-A.
  • COF-320-A exhibits unconventional, multi-step gas sorption isotherms due to internal pore expansion.
  • The pore expansion in COF-320-A can occur continuously (crystal-to-amorphous) or discontinuously (crystal-to-crystal), or as a mix of both.
  • These transitions differ significantly from rigid COF-320 and other known soft porous crystals.

Conclusions:

  • This work extends the concept of atropisomerism from discrete molecules to infinite crystalline frameworks.
  • The discovery positions COFs within the realm of covalently linked soft porous crystals.
  • These findings open new avenues for advanced applications in gas sorption, separation, and storage using flexible COFs.