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Structure of Conjugated Dienes

Structure of Conjugated Dienes

Introduction
Conjugated dienes are compounds characterized by the presence of alternating double and single bonds. In a conjugated system like 1,3-butadiene, the unhybridized 2p orbital on each carbon overlaps continuously, allowing the π electrons to be delocalized across the entire molecule. In contrast, this type of overlap does not occur in cumulated and isolated dienes, such as 2,3-pentadiene and 1,4-pentadiene, respectively. Instead, the π electrons remain localized between the double...

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

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

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.

Frost Circles for Different Conjugated Systems

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 Overview

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...

Network Covalent Solids

Network Covalent Solids

Network covalent solids contain a three-dimensional network of covalently bonded atoms as found in the crystal structures of nonmetals like diamond, graphite, silicon, and some covalent compounds, such as silicon dioxide (sand) and silicon carbide (carborundum, the abrasive on sandpaper). Many minerals have networks of covalent bonds.
To break or to melt a covalent network solid, covalent bonds must be broken. Because covalent bonds are relatively strong, covalent network solids are typically...

Conformations of Cyclohexane

Conformations of Cyclohexane

Cyclohexane does not exist in a planar form due to the high angle and torsional strain it would experience in the planar structure. Instead, it adopts non-planar chair and boat conformations.
The chair form is the most stable and derives its name from its resemblance to the “easy chair.” In the chair conformation, two carbon atoms are arranged out-of-plane — one above and one below, minimizing the torsional strain. In the chair form, the bond angle is very close to the ideal...

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Related Experiment Video

Updated: Aug 4, 2025

Microfluidic-based Synthesis of Covalent Organic Frameworks COFs: A Tool for Continuous Production of COF Fibers and Direct Printing on a Surface

Microfluidic-based Synthesis of Covalent Organic Frameworks COFs: A Tool for Continuous Production of COF Fibers and Direct Printing on a Surface

Published on: July 10, 2017

Carbazolylene-Ethynylene Macrocycle based Conductive Covalent Organic Frameworks.

Shaofeng Huang¹, Ji Yong Choi¹, Qiucheng Xu¹

¹Department of Chemistry, University of Colorado Boulder, Boulder, CO 80309, USA.

Angewandte Chemie (International Ed. in English)

|March 30, 2023

Summary

Two novel covalent organic frameworks (COFs) exhibit tunable semiconducting properties. Post-synthetic iodine doping enables switchable electrical conductivity in these porous 2D materials.

Keywords:

Alkyne Metathesis Arylene Ethynylene Macrocycle Chemical Doping Covalent Organic Frameworks Electrical Conductivity

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Synthesis of Single-Crystalline Core-Shell Metal-Organic Frameworks

Synthesis of Single-Crystalline Core-Shell Metal-Organic Frameworks

Published on: February 10, 2023

Synthesis and Characterization of Functionalized Metal-organic Frameworks

Synthesis and Characterization of Functionalized Metal-organic Frameworks

Published on: September 5, 2014

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Last Updated: Aug 4, 2025

Microfluidic-based Synthesis of Covalent Organic Frameworks COFs: A Tool for Continuous Production of COF Fibers and Direct Printing on a Surface

Microfluidic-based Synthesis of Covalent Organic Frameworks COFs: A Tool for Continuous Production of COF Fibers and Direct Printing on a Surface

Published on: July 10, 2017

Synthesis of Single-Crystalline Core-Shell Metal-Organic Frameworks

Synthesis of Single-Crystalline Core-Shell Metal-Organic Frameworks

Published on: February 10, 2023

Synthesis and Characterization of Functionalized Metal-organic Frameworks

Synthesis and Characterization of Functionalized Metal-organic Frameworks

Published on: September 5, 2014

Area of Science:

Materials Science
Organic Chemistry
Nanotechnology

Background:

Covalent organic frameworks (COFs) are crystalline porous polymers with tunable structures and properties.
Developing 2D COFs with intrinsic semiconducting properties and accessible channels is crucial for electronic applications.
Shape-persistent macrocycles offer a route to ordered framework construction.

Purpose of the Study:

To synthesize and characterize novel 2D covalent organic frameworks (COFs) with carbazolylene-ethynylene macrocycles.
To investigate the semiconducting properties and porosity of the synthesized COFs.
To explore the potential for electrical conductivity enhancement and tunability through post-synthetic modification.

Main Methods:

Imine condensation reaction for synthesizing azine (MC-COF-1) and imine (MC-COF-2) linked COFs.
Characterization of 2D frameworks, including porosity and channel alignment.
Post-synthetic incorporation of iodine (I2) for doping and conductivity measurements.

Main Results:

Successful synthesis of fully conjugated 2D MC-COFs with high porosity and aligned channels.
MC-COF-1 demonstrated electrical conductivity up to 7.8×10⁻⁴ S/cm upon I2 doping at room temperature.
Switchable conductivity between electron-conducting and insulating states was achieved through doping-regenerating cycles.

Conclusions:

The synthesized 2D COFs possess intrinsic semiconducting properties and are suitable for conductivity enhancement.
Post-synthetic doping with I2 effectively enables electrical conductivity in the porous frameworks.
The ability to switch conductivity opens avenues for developing tunable 2D organic electronic materials.