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Crown Ethers02:36

Crown Ethers

5.1K
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...
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Anionic Chain-Growth Polymerization: Overview01:20

Anionic Chain-Growth Polymerization: Overview

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The polymerization process that involves carbanion as an intermediate is called anionic polymerization. It is also a type of addition or chain-growth polymerization. Anionic polymerization gets initiated by a strong nucleophile such as an organolithium or a Grignard reagent. The most commonly used initiator for anionic polymerization is butyl lithium. Monomers involved in anionic polymerization must possess a vinyl group bonded to one or two electron-withdrawing groups. For instance,...
2.1K
Cationic Chain-Growth Polymerization: Mechanism00:57

Cationic Chain-Growth Polymerization: Mechanism

2.2K
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...
2.2K
Aromatic Hydrocarbon Anions: Structural Overview01:18

Aromatic Hydrocarbon Anions: Structural Overview

2.6K
Neutral hydrocarbons like cyclopentadiene with an odd number of carbon atoms and one intervening CH2 group in the ring are not aromatic. Cyclopentadiene with 4 π electrons does not satisfy the 4n + 2 π electron rule. Additionally, the intervening CH2 group is sp3 hybridized and lacks a vacant p orbital, thereby interrupting the overlap of p orbitals in a continuous manner and preventing the delocalization of π electrons throughout the ring.
Due to the absence of continuous...
2.6K
Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

2.0K
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.
2.0K
Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule02:17

Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule

13.9K
If a set of reactants can yield multiple constitutional isomers, but one of the isomers is obtained as the major product, the reaction is said to be regioselective. In such reactions, bond formation or breaking is favored at one reaction site over others.
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
13.9K

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Updated: Jun 2, 2025

Anionic Polymerization of an Amphiphilic Copolymer for Preparation of Block Copolymer Micelles Stabilized by &#960;-&#960; Stacking Interactions
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Anionic Polymerization of an Amphiphilic Copolymer for Preparation of Block Copolymer Micelles Stabilized by π-π Stacking Interactions

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Anionic modulation induces molecular polarity in a three-component crown ether system.

Feiyan Liu1, Guoyong Chen1, Xiao Liu1

  • 1School of Chemistry and Chemical Engineering, Nanchang University, Nanchang, 330031, People's Republic of China. 352800220014@email.ncu.edu.cn.

Dalton Transactions (Cambridge, England : 2003)
|January 13, 2025
PubMed
Summary

Novel crown ether materials exhibit temperature-induced structural changes, leading to tunable physical properties. One compound shows switchable second harmonic generation (SHG) signals, offering potential for advanced optical applications.

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Highly Stereoselective Synthesis of 1,6-Ketoesters Mediated by Ionic Liquids: A Three-component Reaction Enabling Rapid Access to a New Class of Low Molecular Weight Gelators
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From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding
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Area of Science:

  • Materials Science
  • Crystallography
  • Supramolecular Chemistry

Background:

  • Crown ether phase change materials respond to external stimuli with altered physical properties.
  • Host-guest crown ether complexes offer tunable characteristics for advanced material design.

Purpose of the Study:

  • To design and synthesize novel host-guest crown ether molecules.
  • To investigate the structure-property relationships of these new materials, particularly their phase transitions and optical/dielectric responses.

Main Methods:

  • Synthesis of [(PTFMA)(15-crown-5)ClO4] (1) and [(PTFMA)(15-crown-5)PF6] (2) via reaction of p-trifluoromethylaniline (PTFMA) with 15-crown-5.
  • Characterization using differential scanning calorimetry (DSC) for phase transitions.
  • Evaluation of second harmonic generation (SHG) signals and dielectric response.

Main Results:

  • Compound 1 exhibits a reversible phase transition from a non-centrosymmetric (P21) to a centrosymmetric (P21/c) space group with increasing temperature.
  • This transition in Compound 1 is accompanied by switchable SHG signals and dielectric response.
  • Compound 2 shows reversible phase transitions and dielectric response but lacks switchable SHG signals.

Conclusions:

  • The anion's polarity significantly influences the properties of crown ether complexes, impacting SHG response.
  • These findings provide insights for developing new crown ether complexes with switchable optical properties.
  • The study highlights the potential of designed crown ether materials for applications requiring stimuli-responsive behavior.