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Related Concept Videos

Aromatic Hydrocarbon Anions: Structural Overview01:18

Aromatic Hydrocarbon Anions: Structural Overview

4.2K
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...
4.2K
Criteria for Aromaticity and the Hückel 4n + 2 Rule01:20

Criteria for Aromaticity and the Hückel 4n + 2 Rule

14.5K
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 Hückel’s rule or the 4n +...
14.5K
Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

4.2K
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...
4.2K
Frost Circles for Different Conjugated Systems01:18

Frost Circles for Different Conjugated Systems

4.1K
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.
4.1K
π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds01:14

π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds

2.0K
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...
2.0K
Five-Membered Heterocyclic Aromatic Compounds: Overview01:13

Five-Membered Heterocyclic Aromatic Compounds: Overview

6.0K
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 and Through-Space Interaction between Aromatic Rings in [2.2]Paracyclophanes.

Irena Majerz1, Teresa Dziembowska2

  • 1Faculty of Pharmacy, Wroclaw Medical University , Borowska 211a, 50-556 Wroclaw, Poland.

The Journal of Physical Chemistry. A
|October 1, 2016
PubMed
Summary

The HOMA index indicates reduced aromaticity in [2.2]paracyclophanes. Analyzing interactions with AIM and NCI methods is crucial for understanding these nonbonded forces in cyclophane structures.

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Area of Science:

  • Supramolecular Chemistry
  • Organic Chemistry
  • Computational Chemistry

Background:

  • [2.2]Paracyclophanes are unique molecules featuring two benzene rings bridged by ethylene units.
  • Understanding the electronic properties and intermolecular interactions within these structures is key to their application.
  • Previous studies have explored their synthesis and basic structural features.

Purpose of the Study:

  • To investigate the aromaticity and nonbonded interactions in [2.2]paracyclophanes using computational methods.
  • To determine the extent of aromaticity in the solid state via the HOMA index.
  • To elucidate the nature of interactions between the aromatic rings in various [2.2]paracyclophane derivatives.

Main Methods:

  • Calculation of the HOMA index for solid-state [2.2]paracyclophanes.
  • Application of Atoms in Molecules (AIM) analysis to identify bonding and non-bonding interactions.
  • Utilization of Non-Covalent Interactions (NCI) analysis to visualize inter-ring interactions.
  • Investigation of both crystal structures and computationally optimized geometries.

Main Results:

  • The HOMA index revealed a slight decrease in aromaticity for the studied [2.2]paracyclophanes in the solid state.
  • AIM analysis confirmed the presence of a C···C bond path between the aromatic rings in only a limited number of derivatives.
  • NCI analysis successfully visualized the significant role of dispersion and repulsive forces between the aromatic rings across all investigated [2.2]paracyclophanes.
  • The study identified specific [2.2]paracyclophanes exhibiting distinct interaction patterns.

Conclusions:

  • A combination of AIM and NCI analyses is essential for a comprehensive understanding of nonbonded interactions in [2.2]paracyclophanes.
  • The interplay of attractive and repulsive forces significantly influences the electronic and structural properties of these molecules.
  • The findings provide valuable insights for the rational design and synthesis of novel paracyclophane derivatives with tailored properties.