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Related Concept Videos

Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

3.5K
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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Nomenclature of Alkynes02:39

Nomenclature of Alkynes

18.2K
Alkynes are unsaturated hydrocarbons characterized by the presence of carbon-carbon triple bonds and have a general formula CnH2n-2. The nomenclature of alkynes follows a set of rules similar to alkanes and alkenes; however, alkynes bear the suffix "-yne" instead of "-ane" or "-ene." There are two approaches to naming alkynes:
18.2K
Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

2.1K
Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
2.1K
[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction01:16

[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction

8.0K
The Diels–Alder reaction is an example of a thermal pericyclic reaction between a conjugated diene and an alkene or alkyne, commonly referred to as a dienophile. The reaction involves a concerted movement of six π electrons, four from the diene and two from the dienophile, forming an unsaturated six-membered ring. As a result, these reactions are classified as [4+2] cycloadditions.
8.0K
Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

1.6K
The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
1.6K
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...
3.5K

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Preparation of a Corannulene-functionalized Hexahelicene by CopperI-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units
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Preparation of a Corannulene-functionalized Hexahelicene by CopperI-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units

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Clar theory extended for polyacenes and beyond.

Debojit Bhattacharya1, Anirban Panda, Anirban Misra

  • 1MARS, Texas A&M University at Galveston , Galveston, Texas 77553, United States.

The Journal of Physical Chemistry. A
|May 21, 2014
PubMed
Summary
This summary is machine-generated.

This study extends Clar's sextet theory to explain weak-pairing long bonds in polyacene polymers. This new theory helps understand increasing radicality and aromaticity in longer chains and graphene structures.

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Area of Science:

  • Organic Chemistry
  • Materials Science
  • Theoretical Chemistry

Background:

  • Clar's classical sextet theory describes aromaticity in polycyclic hydrocarbons.
  • Polyacenes exhibit increasing radicality with chain length, posing challenges for existing theories.
  • Understanding bonding in extended polyacene systems is crucial for materials applications.

Purpose of the Study:

  • To extend Clar's sextet theory to incorporate resonance-based weak-pairing long bonds.
  • To apply this extended theory to polyacenes and analyze their electronic and structural properties.
  • To investigate the applicability of this theory to general grapheneic structures with specific boundaries.

Main Methods:

  • Development of an extended theoretical framework based on Clar's sextet rules.
  • Computational modeling and simulation of polyacene chains of varying lengths.
  • Analysis of resonance energies, bond lengths, and local aromaticity indices.

Main Results:

  • The extended theory successfully describes resonance-based weak-pairing long bonds in polyacenes.
  • Calculations show how radicality and aromaticity evolve in polyacenes with increasing chain length.
  • Weak pairing phenomena were also identified in grapheneic structures with zig-zag boundaries.

Conclusions:

  • The extended Clar's sextet theory provides a robust explanation for weak-pairing long bonds in polyacenes.
  • This theoretical advancement is essential for understanding the properties of extended conjugated systems.
  • The findings have implications for designing novel carbon-based materials with tailored electronic properties.