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Related Concept Videos

Aromatic Hydrocarbon Anions: Structural Overview01:18

Aromatic Hydrocarbon Anions: Structural Overview

3.9K
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...
3.9K
Criteria for Aromaticity and the Hückel 4n + 2 Rule01:20

Criteria for Aromaticity and the Hückel 4n + 2 Rule

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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 Hückel’s rule or the 4n +...
13.9K
Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

4.0K
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...
4.0K
Frost Circles for Different Conjugated Systems01:18

Frost Circles for Different Conjugated Systems

3.9K
The inscribed polygon method is consistent with Hückel’s 4n + 2 rule and helps to learn whether the given cyclic compound is aromatic or not. The compound is stable and aromatic if every bonding molecular orbital (MO) is completely filled with a pair of electrons. However, if the non-bonding or antibonding orbitals are filled with electrons, the compound is unstable and not aromatic. Consider the Frost circle diagrams for cycloalkenes containing 4 to 8 carbons.
3.9K
Five-Membered Heterocyclic Aromatic Compounds: Overview01:13

Five-Membered Heterocyclic Aromatic Compounds: Overview

5.8K
Heterocyclic aromatic compounds are cyclic compounds that are aromatic and have one or more heteroatoms—atoms other than carbon, in the ring. Depending upon the number of atoms present in the ring, they can be either five or six-membered. Examples of five-membered heterocyclic aromatic compounds include pyrrole, furan, thiophene, and imidazole. Pyrrole consists of one nitrogen atom having one lone pair of electrons. Furan and thiophene have one oxygen and one sulfur heteroatom,...
5.8K
π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds01:14

π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds

1.9K
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...
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Related Experiment Video

Updated: Feb 18, 2026

Preparation of a Corannulene-functionalized Hexahelicene by CopperI-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units
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Bicyclic Baird-type aromaticity.

Won-Young Cha1, Taeyeon Kim1, Arindam Ghosh2

  • 1Department of Chemistry, Yonsei University, Shinchon-dong 134, Seodaemoongu, Seoul 120-749, Korea.

Nature Chemistry
|November 24, 2017
PubMed
Summary
This summary is machine-generated.

Researchers synthesized novel non-planar organic molecules, dithienothiophene-bridged [34]octaphyrins, demonstrating experimental evidence for bicycloaromaticity. These molecules exhibit distinct aromatic properties based on their oxidation state, offering new insights into aromaticity theory.

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Area of Science:

  • Organic Chemistry
  • Theoretical Chemistry
  • Materials Science

Background:

  • Aromaticity is traditionally linked to planar conjugated macrocycles.
  • Bicycloaromaticity, a theoretical concept, has lacked experimental validation in synthetic organic molecules.
  • Conjugated organic systems offer tunable electronic properties for experimental studies.

Purpose of the Study:

  • To synthesize and characterize novel non-planar organic molecules for studying aromaticity.
  • To experimentally investigate bicycloaromaticity in a synthetic system.
  • To explore the relationship between molecular structure, oxidation state, and aromatic behavior.

Main Methods:

  • Synthesis of dithienothiophene-bridged [34]octaphyrins.
  • Characterization using spectroscopic and electrochemical techniques.
  • Computational analysis to understand electronic structure and aromaticity.

Main Results:

  • Successful synthesis of two purely organic, non-planar [34]octaphyrins.
  • Neutral forms exhibit competing 26 and 34 π-electron circuits.
  • Two-electron oxidation yields triplet biradical species with global aromaticity, supporting Baird's rule.

Conclusions:

  • Experimental demonstration of bicycloaromaticity in synthetic organic molecules.
  • The synthesized octaphyrins provide a platform for studying oxidation-dependent aromaticity.
  • These findings advance the understanding of aromaticity beyond traditional planar systems.