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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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Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

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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...
2.8K
Radicals: Electronic Structure and Geometry01:07

Radicals: Electronic Structure and Geometry

4.0K
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...
4.0K
Woodward–Hoffmann Selection Rules and Microscopic Reversibility01:34

Woodward–Hoffmann Selection Rules and Microscopic Reversibility

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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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Radical Reactivity: Steric Effects01:10

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The presence of electron-donating, electron-withdrawing, or conjugating groups adjacent to a radical center, imparts electronic stabilization to the radicals. Examples of such electronically-stabilized radicals are triphenylmethyl, tetramethylpiperidine‐N‐oxide, and 2,2‐diphenyl‐1‐picrylhydrazyl. These radicals are remarkably stable and are known as persistent radicals. Some of the persistent radicals can even be isolated and purified.
Along with electronic...
1.9K
Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

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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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Peri-pentacene and Peri-hexacene Diradicaloids.

Ya Zou1, Liuying Jiao1, Yi Han1

  • 1Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543, Singapore.

Journal of the American Chemical Society
|September 24, 2024
PubMed
Summary

Stable derivatives of peri-pentacene and peri-hexacene were synthesized, exhibiting significant diradical character and narrow singlet-triplet energy gaps. These compounds show remarkable stability in ambient conditions, advancing research on graphene nanoribbon models.

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Area of Science:

  • Organic Chemistry
  • Materials Science
  • Nanotechnology

Background:

  • Peri-acenes serve as crucial models for understanding zigzag-edged graphene nanoribbons.
  • The synthesis of peri-acenes is notoriously challenging, limiting their study and application.

Purpose of the Study:

  • To synthesize stable derivatives of peri-pentacene (Peri-P) and peri-hexacene (Peri-H).
  • To investigate the stability, electronic properties, and structural characteristics of these novel peri-acene compounds.

Main Methods:

  • Kinetic blocking and synergistic captodative effects were employed for synthesis.
  • Stability was assessed under ambient air and light conditions.
  • Diradical character (y0), singlet-triplet energy gaps, X-ray crystallography, bond-length analysis, and theoretical calculations were utilized.

Main Results:

  • Stable Peri-P and Peri-H derivatives were successfully synthesized.
  • Both compounds exhibited high diradical character (75.4% for Peri-P, 90.7% for Peri-H) and narrow singlet-triplet energy gaps.
  • Peri-H structure confirmed by X-ray crystallography, revealing a dominant five aromatic sextet ring structure.

Conclusions:

  • The developed synthetic strategies enable the creation of stable, high-diradical character peri-acenes.
  • These findings provide valuable insights into the electronic and structural properties of graphene nanoribbon models.
  • Further studies on optical and electrochemical properties are warranted.