Search research articles

ABOUT JoVE

Overview Leadership Blog JoVE Help Center

AUTHORS

Publishing Process Editorial Board Scope & Policies Peer Review FAQ Submit

LIBRARIANS

Testimonials Subscriptions Access Resources Library Advisory Board FAQ

RESEARCH

JoVE Journal Methods Collections JoVE Encyclopedia of Experiments Archive

EDUCATION

JoVE Core JoVE Business JoVE Science Education JoVE Lab Manual Faculty Resource Center Faculty Site

Terms & Conditions of Use

Related Concept Videos

Thermal Electrocyclic Reactions: Stereochemistry

Thermal Electrocyclic Reactions: Stereochemistry

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.

π Molecular Orbitals of 1,3-Butadiene

π Molecular Orbitals of 1,3-Butadiene

Conjugated dienes have lower heats of hydrogenation than cumulated and isolated dienes, making them more stable. The enhanced stabilization of conjugated systems can be understood from their π molecular orbitals.
The simplest conjugated diene is 1,3-butadiene: a four-carbon system where each carbon is sp2-hybridized and has an unhybridized p orbital that contains an unpaired electron. According to molecular orbital theory, atomic orbitals combine to form molecular orbitals such that the number...

Stability of Conjugated Dienes

Stability of Conjugated Dienes

Introduction
A comparison of the enthalpies of hydrogenation of dienes reveals that conjugated dienes release less heat on hydrogenation, rendering them more stable than their nonconjugated analogs.

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...

Photochemical Electrocyclic Reactions: Stereochemistry

Photochemical Electrocyclic Reactions: Stereochemistry

The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation

Reduction of Benzene to Cyclohexane: Catalytic Hydrogenation

Reduction of Benzene to Cyclohexane: Catalytic Hydrogenation

Unlike the easy catalytic hydrogenation of an alkene double bond, hydrogenation of a benzene double bond under similar reaction conditions does not take place easily. For example, in the reduction of stilbene, the benzene ring remains unaffected while the alkene bond gets reduced. Hydrogenation of an alkene double bond is exothermic and a favorable process. In contrast, to hydrogenate the first unsaturated bond of benzene, an energy input is needed; that is, the process is endothermic. This is...

You might also read

Related Articles

Articles linked to this work by shared authors, journal, and citation graph.

Sort by

Same author

Modular Core-Substituted Naphthalenediimide-Based Metal-Organic Frameworks for Red-Light-Driven Photocatalysis.

Angewandte Chemie (International ed. in English)·2026

Same author

The Synthesis, Construction, and Applications of Benzophenone-Based Porous Polymers.

Chemistry (Weinheim an der Bergstrasse, Germany)·2026

Same author

Supersaturation-Controlled Single-Crystal Growth of Covalent Organic Frameworks with Binary Solvents.

Chemistry (Weinheim an der Bergstrasse, Germany)·2025

Same author

Vinylene-Linked Covalent Organic Frameworks for Visible-Light-Promoted Selective Oxidation of Styrene in Water.

Small (Weinheim an der Bergstrasse, Germany)·2024

Same author

Thermally Activated Photoluminescence Induced by Tunable Interlayer Interactions in Naturally Occurring van der Waals Superlattice SnS/TiS<sub>2</sub>.

Nano letters·2024

Same author

Modular Construction of Vinylene-Linked Covalent Organic Frameworks with Tunable Emission for Tumor Visualization.

Chemistry (Weinheim an der Bergstrasse, Germany)·2024

Search research articles

Related Experiment Video

Updated: Jan 13, 2026

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

Engineering Pyrazine Units in Vinylene-Linked Covalent Organic Frameworks for Efficient C₂H₂/CO₂ Separation.

Mingshuan Yang¹, Shujie Qiao¹, Jun Wang¹

¹College of Materials Science and Engineering, Fuzhou University, Fuzhou, 350108, P. R. China.

Small (Weinheim an Der Bergstrasse, Germany)

|January 12, 2026

Summary

Nitrogen-rich covalent organic frameworks (COFs) show enhanced acetylene/carbon dioxide separation. Increasing pyrazine units in COFs boosts adsorption and separation performance via specific C─H···N interactions.

Keywords:

C2H2/CO2 separation covalent organic framework multi‐pyrazine pore engineering vinylene linkage

More Related Videos

Electrophoretic Crystallization of Ultrathin High-performance Metal-organic Framework Membranes

Electrophoretic Crystallization of Ultrathin High-performance Metal-organic Framework Membranes

Published on: August 16, 2018

Preparation of Hydrophobic Metal-Organic Frameworks via Plasma Enhanced Chemical Vapor Deposition of Perfluoroalkanes for the Removal of Ammonia

Preparation of Hydrophobic Metal-Organic Frameworks via Plasma Enhanced Chemical Vapor Deposition of Perfluoroalkanes for the Removal of Ammonia

Published on: October 10, 2013

Related Experiment Videos

Last Updated: Jan 13, 2026

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

Electrophoretic Crystallization of Ultrathin High-performance Metal-organic Framework Membranes

Electrophoretic Crystallization of Ultrathin High-performance Metal-organic Framework Membranes

Published on: August 16, 2018

Preparation of Hydrophobic Metal-Organic Frameworks via Plasma Enhanced Chemical Vapor Deposition of Perfluoroalkanes for the Removal of Ammonia

Preparation of Hydrophobic Metal-Organic Frameworks via Plasma Enhanced Chemical Vapor Deposition of Perfluoroalkanes for the Removal of Ammonia

Published on: October 10, 2013

Area of Science:

Materials Science
Chemical Engineering
Separation Science

Background:

Separating acetylene (C2H2) from carbon dioxide (CO2) is challenging due to similar molecular properties.
Covalent organic frameworks (COFs) offer tunable porosity and high surface areas for gas adsorption and separation.

Purpose of the Study:

To synthesize and investigate nitrogen-rich, vinylene-linked COFs for effective C2H2/CO2 separation.
To explore the structure-property relationships governing the separation performance.

Main Methods:

Aldol condensation reaction to construct three isostructural pyrazine-containing COFs (PZ-COFs).
Gas adsorption measurements to evaluate C2H2 uptake and selectivity.
Experimental breakthrough tests and theoretical calculations to elucidate separation mechanisms.

Main Results:

Synthesized isostructural PZ-COFs with high surface areas and good stability.
Observed increasing C2H2 adsorption capacity (57.7–107.2 cm3 g–1) and C2H2/CO2 separation efficiency with higher pyrazine content.
Demonstrated that high-density nitrogen sites in COF channels facilitate selective C2H2 adsorption via C─H···N interactions.

Conclusions:

Nitrogen-rich PZ-COFs are promising materials for efficient C2H2/CO2 separation.
The density of nitrogen sites and their interaction with C2H2 are key factors for enhanced separation performance.
Tailoring COF structure, specifically nitrogen content, can optimize gas separation applications.