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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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Frost Circles for Different Conjugated Systems01:18

Frost Circles for Different Conjugated Systems

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

Criteria for Aromaticity and the Hückel 4n + 2 Rule

10.5K
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...
10.5K
Aromatic Compounds: Overview01:25

Aromatic Compounds: Overview

10.6K
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...
10.6K
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
Five-Membered Heterocyclic Aromatic Compounds: Overview01:13

Five-Membered Heterocyclic Aromatic Compounds: Overview

3.9K
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,...
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Preparation of a Corannulene-functionalized Hexahelicene by CopperI-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units
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Aromaticity in Semi-Condensed Figure-Eight Molecules.

Albert Artigas1, Yannick Carissan2, Denis Hagebaum-Reignier2

  • 1Facultat de Ciències, Universitat de Girona, Campus Montilivi, Carrer de Maria Aurèlia Capmany i Farnès 69, 17003, Girona, Catalunya, Spain.

Chemistry (Weinheim an Der Bergstrasse, Germany)
|April 20, 2024
PubMed
Summary

This study investigates electron delocalization and aromaticity in novel figure-eight molecules. Aromaticity character shifts from local to a minor global contribution based on the dihedral angle of connecting bonds.

Keywords:
For the 3D IMS contour mapsaromaticitychiralitycyclophanehelicenehydrocarbons

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Area of Science:

  • Organic Chemistry
  • Theoretical Chemistry
  • Computational Chemistry

Background:

  • Aromaticity is a key concept in chemistry, influencing molecular stability and reactivity.
  • Understanding electron delocalization is crucial for predicting molecular properties.
  • Novel molecular architectures offer opportunities to explore fundamental chemical principles.

Purpose of the Study:

  • To comparatively evaluate electron delocalization and aromaticity in newly synthesized figure-eight molecules.
  • To determine if electron delocalization can occur through stereogenic single bonds.
  • To assess whether aromaticity in these systems is purely local, semi-local, or global.

Main Methods:

  • Synthesis of figure-eight molecules with varying connecting groups (single bonds, para-phenylene, helicene bridges).
  • Comparative evaluation of electron delocalization and aromaticity.
  • Analysis of the influence of dihedral angles at connecting single bonds.

Main Results:

  • Electron delocalization and aromaticity were found to be dependent on the molecular structure and connecting groups.
  • A transition from purely (semi-)local aromaticity to a minor global contribution was observed.
  • The dihedral angle at the connecting single bonds significantly impacts the degree of electron delocalization.

Conclusions:

  • Aromaticity in figure-eight molecules can range from purely (semi-)local to predominantly (semi-)local with a minor global component.
  • Stereogenic single bonds can facilitate some electron delocalization, depending on their conformation.
  • Molecular geometry plays a critical role in governing electron delocalization pathways and aromatic character.