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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.
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Related Experiment Video

Updated: Apr 24, 2026

Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene

Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene

Published on: March 20, 2017

A computational study on a strategy for isolating a stable cyclopentadienyl cation.

Kalon J Iversen¹, David J D Wilson, Jason L Dutton

¹Department of Chemistry, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Victoria 3086 (Australia).

Chemistry (Weinheim an Der Bergstrasse, Germany)

|September 12, 2014

Summary

Researchers computationally explored stable, isolable monocyclic cyclopentadienyl cations. Electron-withdrawing trifluoromethyl groups enhance stability, suggesting these compounds are promising targets for synthesis and isolation at room temperature.

Keywords:

antiaromaticity carbocations theoretical chemistry

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Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene

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Area of Science:

Computational Chemistry
Organic Chemistry
Organometallic Chemistry

Background:

Cyclopentadienyl cations (Cp+) are typically highly reactive intermediates.
Stable aromatic systems are crucial for synthetic applications and fundamental studies.
Previous research has focused on stabilizing reactive organic species through electronic effects.

Purpose of the Study:

To computationally investigate the feasibility of creating a stable, isolable monocyclic cyclopentadienyl cation.
To identify specific substituents that could confer sufficient stability for isolation at ambient temperatures.
To evaluate the potential stability of these modified Cp+ derivatives by comparing them to known stable ring systems.

Main Methods:

Utilized computational chemistry methods to model and analyze molecular properties.
Focused on the electronic effects of electron-withdrawing groups, specifically trifluoromethyl (CF3) substituents.
Evaluated stability using key electronic parameters such as Highest Occupied Molecular Orbital-Lowest Unoccupied Molecular Orbital (HOMO-LUMO) energy gaps and singlet-triplet energy gaps.

Main Results:

Identified a specific cyclopentadienyl cation derivative with judiciously placed trifluoromethyl groups that exhibits enhanced stability.
Computational analysis indicates that this derivative's stability may approach that of isolobal and isolatable borole rings.
The calculated HOMO-LUMO and singlet-triplet gaps suggest a significant stabilization effect from the CF3 substituents.

Conclusions:

Monocyclic cyclopentadienyl cations can be computationally designed to achieve stability suitable for isolation and handling at ambient temperatures.
The strategic incorporation of electron-withdrawing trifluoromethyl groups is a viable approach to stabilize these reactive species.
These stabilized Cp+ derivatives represent attractive targets for future synthetic efforts and experimental validation.