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Related Concept Videos

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...
Five-Membered Heterocyclic Aromatic Compounds: Overview01:13

Five-Membered Heterocyclic Aromatic Compounds: Overview

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, respectively.
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...
Criteria for Aromaticity and the Hückel 4n + 2 Rule01:20

Criteria for Aromaticity and the Hückel 4n + 2 Rule

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 + 2 rule.
Electrophilic Aromatic Substitution: Overview01:16

Electrophilic Aromatic Substitution: Overview

In an electrophilic aromatic substitution reaction, an electrophile substitutes for a hydrogen of an aromatic compound.
π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds01:14

π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds

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 annulenes. In...

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Synthesis of Pyrrole-Sharing Fused Porphyrinoid Hybrids by Post-fabrication of Ni(II) Porphyrins.

Angewandte Chemie (International ed. in English)·2023
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Di(p-dibenzi)[40]decaphyrin(1.0.0.0.0.1.0.0.0.0) Pd<sup>II</sup> Complex: A Weakly Hückel 38π-Aromatic Macrocycle.

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Cyclic Azobenzene-BODIPY Hybrids.

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Stable Antiaromatic [24]Hexaphyrin(1.1.0.0.1.0) and Its Metal Complexes.

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Synthesis of Naphthalene- and Phenanthrene-Fused Smaragdyrins and Their BF<sub>2</sub> Complexes.

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Publisher Correction: Doubly N-confused and ring-contracted [24] hexaphyrin Pd-complexes as stable antiaromatic N-confused expanded porphyrins.

Nature communications·2023

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Updated: Jun 3, 2026

[(DPEPhos)(bcp)Cu]PF6: A General and Broadly Applicable Copper-Based Photoredox Catalyst
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[(DPEPhos)(bcp)Cu]PF6: A General and Broadly Applicable Copper-Based Photoredox Catalyst

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Expanded porphyrins and aromaticity.

Atsuhiro Osuka1, Shohei Saito

  • 1Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan. osuka@kuchem.kyoto-u.ac.jp

Chemical Communications (Cambridge, England)
|March 16, 2011
PubMed
Summary

Meso-aryl expanded porphyrins, which have more than five pyrrolic units, are versatile platforms for creating aromatic, antiaromatic, and radical species. These porphyrins also enable the study of topologically twisted molecules exhibiting Möbius aromaticity.

Area of Science:

  • Organic Chemistry
  • Supramolecular Chemistry
  • Materials Science

Background:

  • Expanded porphyrins are porphyrin analogues with more than five pyrrolic units.
  • These macrocycles offer unique electronic and topological properties.
  • Meso-aryl substitution provides a handle for tuning these properties.

Purpose of the Study:

  • To explore meso-aryl substituted expanded porphyrins as a platform for novel chemical species.
  • To investigate the potential for realizing diverse aromatic, antiaromatic, and radical species.
  • To examine the creation of topologically twisted molecules with Möbius aromaticity.

Main Methods:

  • Synthesis of meso-aryl substituted expanded porphyrins.
  • Spectroscopic characterization (UV-Vis, NMR, EPR).

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Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach
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  • Computational modeling to understand electronic and topological properties.

    • Main Results:

    • Successful synthesis of a series of meso-aryl expanded porphyrins.
    • Demonstration of diverse aromatic, antiaromatic, and stable radical species.
    • Observation of unique topological features, including Möbius aromaticity.

    Conclusions:

    • Meso-aryl expanded porphyrins are highly versatile platforms for fundamental chemical exploration.
    • These compounds provide access to exotic electronic and topological states.
    • Further research into their applications in materials science and catalysis is warranted.