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Crown Ethers

Crown Ethers

Crown ethers are cyclic polyethers that contain multiple oxygen atoms, usually arranged in a regular pattern. The first crown ether was synthesized by Charles Pederson while working at DuPont in 1967. For this work, Pedersen was co-awarded the 1987 Nobel Prize in Chemistry. Crown ethers are named using the formula x-crown-y, where x is the total number of atoms in the ring and y is the number of ether oxygen atoms. The term 'crown' refers to the crown-like shape that these ether molecules take.

Cationic Chain-Growth Polymerization: Mechanism

Cationic Chain-Growth Polymerization: Mechanism

The cationic polymerization mechanism consists of three steps: initiation, propagation, and termination. In the initiation step of the polymerization process, the π bond of a monomer gets protonated by the Lewis acid catalyst, which is formed from boron trifluoride and water. The protonation of the π bond generates a carbocation stabilized by the electron‐donating group. In the propagation step, the π bond of the second monomer acts as a nucleophile and attacks the generated carbocation,...

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 with both...

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.

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.

Olefin Metathesis Polymerization: Ring-Opening Metathesis Polymerization (ROMP)

Olefin Metathesis Polymerization: Ring-Opening Metathesis Polymerization (ROMP)

Ring-opening metathesis polymerization or ROMP involves strained cycloalkenes as starting materials. The mechanism of ROMP proceeds by reacting cycloalkene with Grubbs catalyst to give metallacyclobutane intermediate which undergoes a ring-opening reaction to form new carbene. The new carbene reacts with another molecule of cycloalkene. Repetition of these steps leads to the formation of an unsaturated open-chain polymer product. All these steps are reversible, however, relieving the ring...

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Related Experiment Video

Updated: May 9, 2026

Depolymerizable Olefinic Polymers Based on Fused-Ring Cyclooctene Monomers

Depolymerizable Olefinic Polymers Based on Fused-Ring Cyclooctene Monomers

Published on: December 16, 2022

Polymeric pseudo-crown ether for cation recognition via cation template-assisted cyclopolymerization.

Takaya Terashima¹, Minami Kawabe, Yuichiro Miyabara

¹Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan.

Nature Communications

|August 10, 2013

Summary

Researchers developed cation template-assisted cyclopolymerization to create polymeric pseudo-crown ethers. This efficient method yields polymers with large in-chain cavities for selective molecular recognition.

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Area of Science:

Polymer Chemistry
Supramolecular Chemistry
Organic Synthesis

Background:

Cyclopolymerization typically yields polymers with cyclic structures but often requires complex monomer design.
Achieving large in-chain cyclic structures in polymers usually necessitates elaborate monomer synthesis.
The functionality of cyclopolymers with multiple large rings is promising but underexplored due to synthetic challenges.

Purpose of the Study:

To develop an efficient strategy for synthesizing cyclopolymers with large in-chain cavities.
To explore cation template-assisted cyclopolymerization for creating polymeric pseudo-crown ethers.
To enable selective molecular recognition using functional cyclopolymers.

Main Methods:

Utilized cation template-assisted cyclopolymerization of poly(ethylene glycol) dimethacrylates.
Employed size-fit metal cations to direct the conformation of divinyl monomers.
Investigated the formation of pseudo-cyclic conformations facilitating intramolecular cyclization.

Main Results:

Successfully synthesized polymeric pseudo-crown ethers with large in-chain cavities (up to 30-membered rings).
Demonstrated an efficient, one-pot method combining supramolecular and polymer chemistry principles.
Showcased the direct transformation of common reagents into functional cyclopolymers using simple templates.

Conclusions:

Cation template-assisted cyclopolymerization is an effective route to functional cyclopolymers with large cavities.
This approach simplifies the synthesis of complex polymeric structures for molecular recognition applications.
The strategy offers a versatile platform for creating novel functional polymers from readily available materials.