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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...
2.8K
Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

2.9K
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...
2.9K
π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds01:14

π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds

1.2K
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...
1.2K
Criteria for Aromaticity and the Hückel 4n + 2 Rule01:20

Criteria for Aromaticity and the Hückel 4n + 2 Rule

10.9K
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...
10.9K
Frost Circles for Different Conjugated Systems01:18

Frost Circles for Different Conjugated Systems

2.8K
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.
2.8K
Electron Paramagnetic Resonance (EPR) Spectroscopy: Organic Radicals01:17

Electron Paramagnetic Resonance (EPR) Spectroscopy: Organic Radicals

2.6K
Ideally, an unpaired electron shows a single peak in the EPR spectrum due to the transition between the two spin energy states. However, coupling interactions can occur between the spins of the unpaired electron and any neighboring spin-active nuclei. This hyperfine coupling results in hyperfine splitting, where the EPR signal is split into multiplets. The signals split into 2nI + 1 peaks, where n is the number of equivalent nuclei and I is the nuclear spin. These splitting patterns provide...
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Related Experiment Video

Updated: Jul 29, 2025

Preparation of a Corannulene-functionalized Hexahelicene by CopperI-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units
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Preparation of a Corannulene-functionalized Hexahelicene by CopperI-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units

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Xanthene-Separated 24 π-Electron Antiaromatic Rosarin Dimer.

Seokwon Lee1, Yuying Wang2, Ranjan Dutta3

  • 1Department of Chemistry, Spectroscopy Laboratory for Functional π-Electronic Systems, Yonsei University, Seoul, 03722, Korea.

Chemistry (Weinheim an Der Bergstrasse, Germany)
|May 19, 2023
PubMed
Summary

This study reports a covalently linked rosarin dimer, demonstrating reduced antiaromaticity at low temperatures due to intramolecular interactions. This finding offers insights into the behavior of stacked antiaromatic molecules.

Keywords:
antiaromaticitycryogenicoptical propertyπ-π stacked dimer

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Preparation of a Corannulene-functionalized Hexahelicene by CopperI-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units
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Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
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Area of Science:

  • Organic Chemistry
  • Materials Science
  • Computational Chemistry

Background:

  • Antiaromatic molecules exhibit high reactivity and narrow HOMO-LUMO gaps.
  • Stacking of antiaromatic molecules may induce three-dimensional aromaticity through frontier orbital interactions.

Purpose of the Study:

  • To investigate the properties of a covalently linked π-π stacked rosarin dimer.
  • To explore the impact of temperature on the antiaromaticity of the dimer.

Main Methods:

  • Experimental examination using steady-state absorption and transient absorption spectroscopy.
  • Theoretical analysis via quantum chemical calculations, including TD-DFT, AICD, and NICS.

Main Results:

  • The rosarin dimer exhibits diminished antiaromaticity at 77 K compared to its monomer.
  • Intramolecular interactions between rosarin subunits are identified as the cause for reduced antiaromaticity.

Conclusions:

  • Covalently linked π-π stacking can modulate the antiaromatic character of molecules.
  • Temperature-dependent intramolecular interactions play a crucial role in the electronic properties of stacked antiaromatic systems.