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 and Photochemical Electrocyclic Reactions: Overview

Thermal and Photochemical Electrocyclic Reactions: Overview

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.

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

Cycloaddition Reactions: Overview

Cycloaddition Reactions: Overview

Cycloadditions are one of the most valuable and effective synthesis routes to form cyclic compounds. These are concerted pericyclic reactions between two unsaturated compounds resulting in a cyclic product with two new σ bonds formed at the expense of π bonds. The [4 + 2] cycloaddition, known as the Diels–Alder reaction, is the most common. The other example is a [2 + 2] cycloaddition.

[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.

Cycloaddition Reactions: MO Requirements for Thermal Activation

Cycloaddition Reactions: MO Requirements for Thermal Activation

Thermal cycloadditions are reactions where the source of activation energy needed to initiate the reaction is provided in the form of heat. A typical example of a thermally-allowed cycloaddition is the Diels–Alder reaction, which is a [4 + 2] cycloaddition. In contrast, a [2 + 2] cycloaddition is thermally forbidden.

Cycloaddition Reactions: MO Requirements for Photochemical Activation

Cycloaddition Reactions: MO Requirements for Photochemical Activation

Some cycloaddition reactions are activated by heat, while others are initiated by light. For example, a [2 + 2] cycloaddition between two ethylene molecules occurs only in the presence of light. It is photochemically allowed but thermally forbidden.

You might also read

Related Articles

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

Sort by

Same author

Dynamic Self-Healing Polymer Architectures for High-Performance Flexible Sensing.

Advanced materials (Deerfield Beach, Fla.)·2026

Same author

Moisture-Gated Synergistic Rapid Crystal-to-Liquid Transition in Pyridinium Halide Crystals via [2 + 2] Photocycloaddition.

Small (Weinheim an der Bergstrasse, Germany)·2026

Same author

A Closed-Loop Recyclable Hydrogel With Temperature-Programmable Photomorphing Enabled by a Dynamic Spiropyran-Disulfide Network.

ChemSusChem·2026

Same author

Biomimetic Supramolecular Assemblies With Programmable Structural and Chiroptical Dynamics.

Angewandte Chemie (International ed. in English)·2026

Same author

Supramolecular polymerization couples constitutional adaptability and fluorescence response in a dynamic covalent library.

Chemical communications (Cambridge, England)·2026

Same author

Aspect ratio-dependent twisting motions in photomechanical molecular crystal ribbons <i>via</i> solid-state [2+2] photodimerization.

Chemical communications (Cambridge, England)·2026

Same journal

Proton Transfer Shuttle Mediated Dormant-Active Balance for Accelerated and Controlled Polymerization of N-Carboxyanhydrides.

Angewandte Chemie (International ed. in English)·2026

Same journal

Chloride-Regulated Depolymerization of Aluminosilicate Networks for Fast Ion Transport Compliant Interfaces in Sustainable All-Solid-State Sodium Batteries.

Angewandte Chemie (International ed. in English)·2026

Same journal

Asymmetric Zn─N<sub>2</sub>O-Coordinated Hydrogen-Bonded Organic Frameworks for Electrochemical Hydrogen Peroxide Production and Wastewater Purification.

Angewandte Chemie (International ed. in English)·2026

Same journal

Photocatalytic Cascade Nitrogen Fixation for Selective Purification of Methane-Rich Coal-Bed Gas Over a Bimetallic MOF.

Angewandte Chemie (International ed. in English)·2026

Same journal

Scalable Art-Inspired Tessellated Covalent Organic Framework Membranes Enable Highly Selective Ion Separation.

Angewandte Chemie (International ed. in English)·2026

Same journal

Layered Copper-Anthraquinone Coordination Polymer Cathode Leveraging Dual-Redox Sites and Facilitated Ion Diffusion for High-Performance Lithium-Ion Batteries.

Angewandte Chemie (International ed. in English)·2026

See all related articles

Search research articles

Related Experiment Video

Updated: May 3, 2026

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

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

Published on: September 18, 2016

A half adder based on a photochemically driven [2]rotaxane

Da-Hui Qu¹, Qiao-Chun Wang, He Tian

¹Laboratory for Advanced Materials and Institute of Fine Chemicals, East China University of Science & Technology, Shanghai.

Angewandte Chemie (International Ed. in English)

|July 23, 2005

Summary

No abstract available in PubMed .

More Related Videos

Self-assembling Morphologies Obtained from Helical Polycarbodiimide Copolymers and Their Triazole Derivatives

Self-assembling Morphologies Obtained from Helical Polycarbodiimide Copolymers and Their Triazole Derivatives

Published on: February 7, 2017

Light-driven Molecular Motors on Surfaces for Single Molecular Imaging

Light-driven Molecular Motors on Surfaces for Single Molecular Imaging

Published on: March 13, 2019

Related Experiment Videos

Last Updated: May 3, 2026

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

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

Published on: September 18, 2016

Self-assembling Morphologies Obtained from Helical Polycarbodiimide Copolymers and Their Triazole Derivatives

Self-assembling Morphologies Obtained from Helical Polycarbodiimide Copolymers and Their Triazole Derivatives

Published on: February 7, 2017

Light-driven Molecular Motors on Surfaces for Single Molecular Imaging

Light-driven Molecular Motors on Surfaces for Single Molecular Imaging

Published on: March 13, 2019