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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...
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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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Woodward–Hoffmann Selection Rules and Microscopic Reversibility01:34

Woodward–Hoffmann Selection Rules and Microscopic Reversibility

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Electrocyclic reactions, cycloadditions, and sigmatropic rearrangements are concerted pericyclic reactions that proceed via a cyclic transition state. These reactions are stereospecific and regioselective. The stereochemistry of the products depends on the symmetry characteristics of the interacting orbitals and the reaction conditions. Accordingly, pericyclic reactions are classified as either symmetry-allowed or symmetry-forbidden. Woodward and Hoffmann presented the selection criteria for...
3.7K
Aromatic Hydrocarbon Anions: Structural Overview01:18

Aromatic Hydrocarbon Anions: Structural Overview

3.5K
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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VSEPR Theory and the Effect of Lone Pairs04:01

VSEPR Theory and the Effect of Lone Pairs

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Effect of Lone Pairs of Electrons on Molecule Geometry
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Hückel's Rule Diagram of π MOs: Frost Circle01:08

Hückel's Rule Diagram of π MOs: Frost Circle

5.4K
The Frost circle or the inscribed polygon method is a graphical method for determining the relative energies of π molecular orbitals (MOs) for planar, fully conjugated, and monocyclic compounds. This method was first described by A. A. Frost and Boris Musulin in 1953.
A Frost circle is constructed by drawing a polygon whose number of edges is equal to the number of carbons of the given cyclic system, with one of the vertices pointing down. Then, a circle is drawn enclosing the polygon so that...
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The Topology of Molecules with Twelve Fused Phenyl Rings ([12]Circulenes): Rings, Infinitenes, and Möbius Infinitenes.

The Journal of organic chemistry·2023
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Chiral Superbases with Extended Hydrogen Bond Networks.

The Journal of organic chemistry·2019
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Updated: Jan 1, 2026

Stable DNA Motifs, 1D and 2D Nanostructures Constructed from Small Circular DNA Molecules
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Cycloparaphenylene Lemniscates and Trefoils.

Steven M Bachrach1

  • 1School of Science , Monmouth University , 400 Cedar Avenue , West Long Branch , New Jersey 07764 , United States.

The Journal of Organic Chemistry
|December 21, 2019
PubMed
Summary

Researchers studied cycloparaphenylene lemniscates and trefoils, finding that increasing loop size reduces ring strain energy (RSE). Nitrogen substitution creates a more planar, ribbon-like structure with lower RSEs.

Area of Science:

  • Organic Chemistry
  • Computational Chemistry
  • Materials Science

Background:

  • Cycloparaphenylenes (CPPs) are a class of molecular architectures with unique structural and electronic properties.
  • Recently synthesized cycloparaphenylene lemniscates (G) and trefoils (E) present novel topological structures for investigation.
  • Understanding the relationship between structure, strain, and substitution is crucial for designing new materials.

Purpose of the Study:

  • To computationally explore variants of cycloparaphenylene lemniscates (G) with different loop sizes and linkage bonds.
  • To investigate the impact of nitrogen substitution on the structure and ring strain energy (RSE) of lemniscates and trefoils.
  • To correlate structural modifications with changes in molecular strain and planarity.

Main Methods:

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  • Density functional theory (DFT) calculations were performed using the ωB97X-D/6-311G(d) level of theory.
  • Geometric optimizations and frequency calculations were used to determine stable structures and RSEs.
  • Analysis of structural parameters, including planarity and bond lengths, was conducted.

Main Results:

  • Lemniscates (G) with four to eight phenyl rings adopted a figure-eight shape, irrespective of the N-N, C═C, or B-N linkage.
  • Ring strain energy (RSE) decreased systematically with increasing loop size for lemniscates.
  • Selective nitrogen substitution at ortho positions induced planarity, leading to ribbon-like structures and reduced RSEs in both lemniscates and trefoils (E).

Conclusions:

  • The RSE of cycloparaphenylene lemniscates is primarily dependent on loop size rather than the linkage bond type.
  • Nitrogen substitution offers a viable strategy to control the planarity and reduce the strain energy of these molecular architectures.
  • These findings provide insights into the design principles for novel strained organic materials with tunable properties.