Related Experiment Video
Updated: Jun 23, 2026
09:35
Preparation of a Corannulene-functionalized Hexahelicene by Copper(I)-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units
Published on: September 18, 2016
Electronic Structure Determines Geometry: Bond Length Alternating in Cyclo[2n]carbons
Xi Chen1,2,3, Xueyuan Yan1, Zihan Liu3
1College of Chemistry & Chemical and Environmental Engineering, Weifang University, Weifang, Shandong 261061, China.
The Journal of Physical Chemistry. A
|October 3, 2024
Summary
Electron correlation, not geometry, causes dual antiaromaticity in cyclo[2n]carbons. Density Functional Theory (DFT) is reliable for larger cyclocarbons but requires caution for smaller ones like C6.
Area of Science:
- * Computational chemistry
- * Theoretical chemistry
- * Organic chemistry
Background:
- * The relationship between electronic structure and molecular geometry is a long-standing question.
- * Cyclo[2n]carbons exhibit dual antiaromaticity, but its origin remains debated.
- * Previous studies have not definitively distinguished between geometric and electronic factors.
Purpose of the Study:
- * To elucidate the origin of dual antiaromaticity in cyclo[2n]carbons.
- * To investigate the role of electron correlation versus geometric symmetry.
- * To assess the reliability of Density Functional Theory (DFT) for studying these systems.
Main Methods:
- * Density Functional Theory (DFT) calculations.
- * Density Matrix Renormalization Group (DMRG) with Complete Active Space Self-Consistent Field (CASSCF) methods.
- * Comparative analysis of electronic structure and geometric symmetry.
Main Results:
- * Dual antiaromaticity in even-membered cyclo[2n]carbons is primarily driven by electron correlation effects.
- * Geometric symmetry alone does not explain the observed dual antiaromaticity.
- * Electron correlation-stabilized dual antiaromaticity is a key concept.
- * DFT is accurate for cyclocarbons larger than C14.
- * DFT inaccurately predicts the structure of C6, highlighting limitations for smaller systems.
Conclusions:
- * Electron correlation is the essential factor for dual antiaromaticity in cyclo[2n]carbons.
- * The concept of electron correlation-stabilized dual antiaromaticity provides a new perspective.
- * Caution is advised when using DFT for small cyclocarbon systems; DMRG-CASSCF offers higher accuracy.
Related Concept Videos
02:37VSEPR Theory
Valence shell electron-pair repulsion theory (VSEPR theory) enables us to predict the molecular structure around a central atom from an examination of the number of bonds and lone electron pairs in its Lewis structure. The VSEPR model assumes that electron pairs in the valence shell of a central atom will adopt an arrangement that minimizes repulsions between these electron pairs by maximizing the distance between them. The electrons in the valence shell of a central atom form either bonding...
01:20Criteria for Aromaticity and the Hückel 4n + 2 Rule
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 Hückel’s rule or the 4n + 2 rule.
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 Hückel’s rule or the 4n + 2 rule.
01:18Aromatic 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...
Due to the absence of continuous overlap of p...
01:18Frost 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.
01:18Aromatic 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...
Removing one hydrogen from the intervening CH2 group with both...
01:07Radicals: Electronic Structure and Geometry
This lesson delves into the geometry of a radical, which is influenced by the electronic structure of the molecule. The principle is similar to that of a lone pair, where the unpaired electron influences the geometry at the radical center.
Accordingly, the structure of a trivalent radical lies between the geometries of carbocations and carbanions. An sp2-hybridized carbocation is trigonal planar, while an sp3-hybridized carbanion is trigonal pyramidal. Here, the difference in geometry is...
Accordingly, the structure of a trivalent radical lies between the geometries of carbocations and carbanions. An sp2-hybridized carbocation is trigonal planar, while an sp3-hybridized carbanion is trigonal pyramidal. Here, the difference in geometry is...