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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...
2.9K
Aromatic Hydrocarbon Anions: Structural Overview01:18

Aromatic Hydrocarbon Anions: Structural Overview

2.9K
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...
2.9K
π Molecular Orbitals of 1,3-Butadiene01:24

π Molecular Orbitals of 1,3-Butadiene

9.4K
Conjugated dienes have lower heats of hydrogenation than cumulated and isolated dienes, making them more stable. The enhanced stabilization of conjugated systems can be understood from their π molecular orbitals.
The simplest conjugated diene is 1,3-butadiene: a four-carbon system where each carbon is sp2-hybridized and has an unhybridized p orbital that contains an unpaired electron. According to molecular orbital theory, atomic orbitals combine to form molecular orbitals such that the number...
9.4K
Stability of Conjugated Dienes01:28

Stability of Conjugated Dienes

3.5K
Introduction
A comparison of the enthalpies of hydrogenation of dienes reveals that conjugated dienes release less heat on hydrogenation, rendering them more stable than their nonconjugated analogs.
3.5K
π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds01:14

π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds

1.2K
In aromatic compounds, such as benzene, the circulation of (4n + 2) π-electrons sets up a diamagnetic or diatropic ring current around the perimeter of the molecule. This current induces a magnetic field that opposes the external field inside the ring and reinforces it on the outside. The protons in benzene are deshielded and exhibit high chemical shifts in the range 6.5–8.5 ppm. The shielding effect at the center of the ring is evident in complex aromatic molecules, such as...
1.2K
Criteria for Aromaticity and the Hückel 4n + 2 Rule01:20

Criteria for Aromaticity and the Hückel 4n + 2 Rule

11.0K
Like benzene, cyclobutadiene and cyclooctatetraene are cyclic compounds with alternate single and double bonds. However, their chemical behavior differs from benzene, as they are unstable and not aromatic. So, what are the structural characteristics of unsaturated compounds categorized as aromatic?  
For the first time, Eric Hückel, a German chemical physicist, derived a set of structural features for a compound to be classified as aromatic. This is now known as...
11.0K

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Preparation of a Corannulene-functionalized Hexahelicene by CopperI-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units
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A π-Extended Pentadecabenzo[9]Helicene.

Yun-Jia Shen1, Nai-Te Yao1, Li-Na Diao1

  • 1College of Chemistry, Beijing Normal University, No. 19, XinJieKouWai St, HaiDian District, Beijing, 100875, P. R. China.

Angewandte Chemie (International Ed. in English)
|February 15, 2023
PubMed
Summary

Researchers synthesized a new chiral nanographene, EP9H, featuring a pentadecabenzo[9]helicene core. This molecule exhibits near-infrared fluorescence and remarkable chiroptical properties, making it a promising material for advanced applications.

Keywords:
CPLChiralHeliceneNanographeneπ-Extended

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Area of Science:

  • Organic Chemistry
  • Materials Science
  • Nanotechnology

Background:

  • Helicenes are polycyclic aromatic hydrocarbons known for their unique helical structures.
  • Chiral organic molecules with extended pi-conjugated systems are of interest for optoelectronic applications.

Purpose of the Study:

  • To synthesize and characterize a novel chiral nanographene with a pentadecabenzo[9]helicene core.
  • To investigate the photophysical and chiroptical properties of the synthesized nanographene.

Main Methods:

  • Synthesis of the novel chiral nanographene (EP9H).
  • Single-crystal X-ray diffraction for structural confirmation.
  • Spectroscopic techniques (fluorescence, CD) and cyclic voltammetry for property analysis.

Main Results:

  • Successful synthesis and full characterization of EP9H, confirming its helical structure.
  • EP9H exhibits near-infrared fluorescence (λem = 684 nm) with a quantum yield of 0.10.
  • The molecule displays seven redox states and significant circular dichroism signals.
  • EP9H shows an outstanding |glum| value of 4.50×10⁻² and BCPL of 304 M⁻¹ cm⁻¹.

Conclusions:

  • The novel chiral nanographene EP9H possesses a unique helical structure and promising optoelectronic properties.
  • Its strong chiroptical activity and NIR emission make it a potential candidate for advanced materials.
  • Further research into its applications in areas like organic electronics and sensing is warranted.