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Related Concept Videos

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 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...
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...
Basicity of Heterocyclic Aromatic Amines01:25

Basicity of Heterocyclic Aromatic Amines

Heterocyclic amines, where the N atom is a part of an alicyclic system, are similar in basicity to alkylamines. Interestingly, the heterocyclic amine having a nitrogen atom as part of an aromatic ring has much less basicity than its corresponding alicyclic counterpart. For this reason, as presented in Figure 1, piperidine (pKb = 2.8) is significantly more basic than pyridine (pKb = 8.8).
Aromatic Compounds: Overview01:25

Aromatic Compounds: Overview

In general, the term ‘aromatic’ indicates a pleasant smell or fragrance from fresh flowers, freshly prepared coffee, etc. In the early history of organic chemistry, many benzene derivatives were isolated from the pleasant odor oils of the plants. For example, vanillin was isolated from the oil of vanilla, methyl salicylate from the oil of wintergreen, and cinnamaldehyde from the oil of cinnamon. They all had a pleasant odor; hence the name aromatic was given.
In 1825, Faraday isolated benzene...
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.

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Related Experiment Video

Updated: Jul 14, 2026

Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach
14:11

Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach

Published on: June 10, 2021

Aromatic and nonaromatic pyriporphyrins.

Timothy D Lash1, Komal Pokharel, Jill M Serling

  • 1Department of Chemistry, Illinois State University, Normal, Illinois 61790-4160, USA. tdlash@ilstu.edu

Organic Letters
|July 3, 2007
PubMed
Summary

Researchers synthesized novel pyriporphyrins with varied pyridine orientations using a

Area of Science:

  • Organic Chemistry
  • Porphyrin Chemistry
  • Heterocyclic Chemistry

Background:

  • Porphyrins are vital macrocyclic compounds with diverse applications.
  • Exploring modified porphyrin structures like pyriporphyrins can lead to new functionalities.
  • Controlling the orientation of heterocyclic moieties within porphyrin frameworks is synthetically challenging.

Purpose of the Study:

  • To synthesize and characterize novel nonaromatic and aromatic pyriporphyrins.
  • To investigate the stability of pyriporphyrins based on substituent placement.
  • To explore synthetic routes for incorporating pyridine into the porphyrin core.

Main Methods:

  • A '3 + 1' synthetic strategy was employed for pyriporphyrin construction.
  • Characterization techniques likely included NMR spectroscopy, mass spectrometry, and UV-Vis spectroscopy.

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[(DPEPhos)(bcp)Cu]PF6: A General and Broadly Applicable Copper-Based Photoredox Catalyst
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  • Specific precursor molecules such as 2,4-pyridinedicarbaldehyde were utilized.

    • Main Results:

    • Three distinct pyriporphyrins with varying pyridine moiety orientations were successfully synthesized.
    • Nonaromatic pyriporphyrins demonstrated stability when phenyl groups were positioned at adjacent meso-positions.
    • An aromatic dihydropyriporphyrin, featuring a CO2Ph protecting group, was also obtained.

    Conclusions:

    • The '3 + 1' strategy is effective for accessing pyriporphyrins with controlled pyridine orientation.
    • Meso-phenyl substitution is crucial for the stability of nonaromatic pyriporphyrin derivatives.
    • The synthesis of an aromatic dihydropyriporphyrin highlights potential for further functionalization.