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Related Concept Videos

Cycloaddition Reactions: MO Requirements for Thermal Activation01:16

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: Overview01:16

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.
Cycloaddition Reactions: MO Requirements for Photochemical Activation01:12

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.
Photochemical Electrocyclic Reactions: Stereochemistry01:26

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
[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction01:16

[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.
Thermal and Photochemical Electrocyclic Reactions: Overview01:26

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.

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Related Experiment Video

Updated: Jul 1, 2026

Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene
09:45

Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene

Published on: March 20, 2017

Charge transfer chromophore-stopped [2]rotaxane through [2 + 2] cycloaddition.

Weidong Zhou1, Jialiang Xu, Haiyan Zheng

  • 1Beijing National Laboratory for Molecular Science, Chinese Academy of Sciences and Graduate school of Chinese Academy of Sciences, Beijing 100190, PR China.

The Journal of Organic Chemistry
|September 11, 2008
PubMed
Summary

Synthesized novel [2]rotaxanes using a high-yield cycloaddition reaction. Developed two molecular shuttles that change shape based on solvent, demonstrating controlled molecular movement.

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Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides Mediated by Ni/Zn Complexes
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Area of Science:

  • Supramolecular Chemistry
  • Organic Synthesis

Background:

  • Charge-transfer chromophores are crucial for molecular electronics.
  • Rotaxanes are mechanically interlocked molecules with potential applications in nanotechnology.
  • Molecular shuttles offer dynamic control over molecular structure and function.

Purpose of the Study:

  • To synthesize novel charge-transfer chromophore-terminated [2]rotaxanes.
  • To construct and investigate two solvent-driving molecular shuttles.
  • To demonstrate controllable conformational changes in molecular shuttles.

Main Methods:

  • High-yield [2 + 2]cycloaddition reaction for rotaxane synthesis.
  • Utilized apolar solvents at room temperature for efficient synthesis.
  • Characterized molecular shuttles' conformations in various solvents.

Main Results:

  • Successfully synthesized three distinct charge-transfer chromophore-terminated [2]rotaxanes.
  • Developed two molecular shuttles exhibiting solvent-dependent conformational changes.
  • Observed clear shuttling movement of the macrocycle in response to solvent polarity.

Conclusions:

  • The developed synthetic route is efficient for creating functional rotaxanes.
  • The molecular shuttles demonstrate responsive and controllable mechanical motion.
  • These findings advance the design of stimuli-responsive molecular machines.