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Related Concept Videos

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...
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...
Structure of Benzene: Molecular Orbital Model01:18

Structure of Benzene: Molecular Orbital Model

According to the molecular orbital (MO) model, benzene has a planar structure with a regular hexagon of six sp2 hybridized carbons. As shown in Figure 1, each carbon is bonded to three other atoms with C–C–C and H–C–C bond angles of 120°. The C–H bond length is 109 pm, and the C–C bond length is 139 pm which is midway between the single bond length of sp3 hybridized carbons (154 pm) and sp2 hybridized carbons (133 pm).
NMR Spectroscopy of Aromatic Compounds01:14

NMR Spectroscopy of Aromatic Compounds

Aromatic compounds can be identified or analyzed using proton NMR and carbon‐13 NMR. Typically, aromatic hydrogens or hydrogens directly bonded to the aromatic rings are strongly deshielded by the aromatic ring current. Therefore, they absorb in the range of 6.5–8.0 ppm in proton NMR spectra. For instance, aromatic hydrogens directly bonded to the benzene ring absorb at 7.3 ppm. However, aromatic hydrogens of larger rings absorb farther upfield or downfield than the ideal range. Consider...
Molecular Orbital Theory II03:51

Molecular Orbital Theory II

Molecular Orbital Energy Diagrams
IR Absorption Frequency: Delocalization01:04

IR Absorption Frequency: Delocalization

Electron delocalization refers to the distribution of electrons across multiple atoms within a molecule rather than being confined to a single atom or bond. This phenomenon is common in systems with conjugated bonds—structures where alternating single and double bonds allow π-electrons to move freely across the network. The movement of electrons stabilizes the molecule and can affect various chemical properties, including vibrational frequencies observed in IR spectroscopy.
In IR spectroscopy,...

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Related Experiment Video

Updated: Jul 16, 2026

Preparation of a Corannulene-functionalized Hexahelicene by Copper(I)-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units
09:35

Preparation of a Corannulene-functionalized Hexahelicene by Copper(I)-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units

Published on: September 18, 2016

A many-electron perspective on aromaticity: investigating delocalization using probability density analysis.

Hannah L Schulz1, Michel V Heinz1, Arne Lüchow1

  • 1Theoretical Chemistry Group, Institute of Physical Chemistry, RWTH Aachen University, Landoltweg 2, 52074 Aachen, Germany. luechow@pc.rwth-aachen.de.

Physical Chemistry Chemical Physics : PCCP
|July 15, 2026
PubMed
Summary

This study uses probability density analysis to define aromaticity, revealing distinct electron rotation patterns in aromatic and antiaromatic systems. These findings offer a new real-space perspective on electron delocalization.

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Last Updated: Jul 16, 2026

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Using Cyclic Voltammetry, UV-Vis-NIR, and EPR Spectroelectrochemistry to Analyze Organic Compounds

Published on: October 18, 2018

Area of Science:

  • Quantum Chemistry
  • Chemical Physics

Background:

  • Aromaticity is crucial in chemistry, defined by cyclic electron delocalization, but lacks a precise, universal definition.
  • Existing measures of aromaticity are insufficient to fully capture its nuances.

Purpose of the Study:

  • To investigate aromaticity using probability density analysis (PDA) for a real-space perspective.
  • To explore electron delocalization in sigma- and pi-aromatic and antiaromatic systems.
  • To generalize Hückel's rule using wave function antisymmetry.

Main Methods:

  • Utilized probability density analysis (PDA) to examine the topology of many-electron probability density |Ψ|².
  • Investigated electron delocalization in various aromatic and antiaromatic systems.
  • Analyzed many-electron rotations as indicators of aromaticity.

Main Results:

  • Discovered characteristic many-electron rotations indicative of cyclic electron delocalization.
  • Aromatic compounds show independent same-spin rotations, unaffected by opposite-spin electrons.
  • Antiaromatic compounds exhibit coupled rotations involving opposite-spin electrons.

Conclusions:

  • PDA provides a valuable real-space method for studying aromaticity.
  • Distinct many-electron rotation patterns differentiate aromatic and antiaromatic systems.
  • The findings offer a deeper understanding of electron delocalization and Hückel's rule.