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Related Concept Videos

Cycloaddition Reactions: Overview01:16

Cycloaddition Reactions: Overview

2.3K
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.
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Cycloaddition Reactions: MO Requirements for Photochemical Activation01:12

Cycloaddition Reactions: MO Requirements for Photochemical Activation

1.7K
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.
1.7K
Cycloaddition Reactions: MO Requirements for Thermal Activation01:16

Cycloaddition Reactions: MO Requirements for Thermal Activation

29.7K
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.
29.7K
Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

1.4K
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
1.4K
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

7.6K
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.
7.6K

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Updated: Apr 24, 2026

Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides Mediated by Ni/Zn Complexes
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Understanding the Propagation Step in a Photoredox Cycloaddition Chain Reaction.

Annemarie A Lee1, Nicole K Oo2, Henry T Eaton1

  • 1Department of Chemistry, Binghamton University, Binghamton, New York 13902, United States.

ACS Catalysis
|April 23, 2026
PubMed
Summary
This summary is machine-generated.

Understanding photoredox chain reactions is key for efficient synthesis. This study reveals the free energy of the propagation step (ΔGprop) as a crucial factor predicting reaction success and quantum yield (QY).

Keywords:
chain reactionkinetic parametersphotoredoxquantum yieldradical cationtransient absorption spectroscopy

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Photogeneration of N-Heterocyclic Carbenes: Application in Photoinduced Ring-Opening Metathesis Polymerization
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Area of Science:

  • Organic Chemistry
  • Photochemistry
  • Catalysis

Background:

  • Photoredox catalysis uses visible light to replace harsh conditions.
  • Photoredox chain reactions offer high productivity but designing them is challenging.
  • A key step is the dark propagation step, where an electron or hole initiates new cycles.

Purpose of the Study:

  • To investigate the kinetics of the propagation step in photoredox chain reactions.
  • To identify key descriptors for designing efficient photoredox chain reactions.
  • To understand the relationship between reaction parameters and chain behavior.

Main Methods:

  • Ruthenium-catalyzed photoredox chain [4 + 2] cyclization.
  • Quantum yield (QY) measurements.
  • Transient absorption spectroscopy (TAS).
  • Electrochemical investigations.
  • Kinetic modeling and computational studies.

Main Results:

  • The free energy for the propagation step (ΔGprop) is the key kinetic descriptor.
  • A linear relationship exists between ΔGprop and the propagation rate constant.
  • ΔGprop accurately predicts the reaction's quantum yield (QY).
  • ΔGprop correlates with the diene's oxidation potential, offering a predictive tool.

Conclusions:

  • ΔGprop is a critical parameter for controlling and predicting photoredox chain reaction efficiency.
  • Diene oxidation potential can serve as a simple molecular predictor for chain reaction behavior.
  • This work provides insights into designing high-productivity photoredox chain reactions.