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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...
Frost Circles for Different Conjugated Systems01:18

Frost Circles for Different Conjugated Systems

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.
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...
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
Crystal Field Theory - Tetrahedral and Square Planar Complexes02:46

Crystal Field Theory - Tetrahedral and Square Planar Complexes

Tetrahedral Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
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...

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Updated: Jun 2, 2026

Spatial Separation of Molecular Conformers and Clusters
10:37

Spatial Separation of Molecular Conformers and Clusters

Published on: January 9, 2014

Ring currents in polycyclic sodium clusters.

Slavko Radenković1, Patrick Bultinck

  • 1Faculty of Science, University of Kragujevac, Kragujevac, Serbia.

The Journal of Physical Chemistry. A
|May 12, 2011
PubMed
Summary
This summary is machine-generated.

This study reveals that while polycyclic sodium clusters exhibit aromaticity, their ring currents are weaker than in similar hydrocarbons. This is primarily due to four HOMO sigma electrons influencing the current density.

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Published on: September 18, 2016

Area of Science:

  • Inorganic Chemistry
  • Theoretical Chemistry
  • Materials Science

Background:

  • Previous work reported molybdenum metalloligands and sodium complexes with 1D hexagonal chains.
  • Aromaticity of hexagonal Na clusters was previously quantified and found comparable to benzenoid hydrocarbons.

Purpose of the Study:

  • To rationalize the aromaticity of polycyclic sodium clusters using current density maps.
  • To investigate the factors determining current density in hexagonal Na systems.

Main Methods:

  • Analysis of current density maps.
  • Computational chemistry techniques to study electronic structure.

Main Results:

  • Polycyclic Na systems sustain diatropic ring currents, but these are weaker than in analogous benzenoid hydrocarbons.
  • Current density in hexagonal Na systems is predominantly determined by four HOMO sigma electrons.

Conclusions:

  • The electronic structure of polycyclic Na clusters supports aromaticity.
  • The weaker aromaticity compared to hydrocarbons is linked to specific electronic configurations, particularly the role of HOMO sigma electrons.