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Related Concept Videos

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
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.
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.
Thermal Electrocyclic Reactions: Stereochemistry01:17

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.
Pericyclic Reactions: Introduction01:17

Pericyclic Reactions: Introduction

Pericyclic reactions are organic reactions that occur via a concerted mechanism without generating any intermediates. The reactions proceed through the movement of electrons in a closed loop to form a cyclic transition state, where rearrangement of the σ and π bonds yields specific products.
Pericyclic reactions can be classified into three categories: electrocyclic reactions, cycloaddition reactions, and sigmatropic rearrangements. Electrocyclic reactions and sigmatropic rearrangements are...
Radical Formation: Homolysis00:54

Radical Formation: Homolysis

A bond is formed between two atoms by sharing two electrons. When this bond is broken by supplying sufficient energy, either two electrons can be taken up by one atom forming ions by the cleavage called heterolysis, or the two electrons are shared by two atoms, with one each creating radicals by the cleavage called homolysis.

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Novel Techniques for Observing Structural Dynamics of Photoresponsive Liquid Crystals
10:35

Novel Techniques for Observing Structural Dynamics of Photoresponsive Liquid Crystals

Published on: May 29, 2018

Ionic liquids: structure and photochemical reactions.

Edward W Castner1, Claudio J Margulis, Mark Maroncelli

  • 1Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854-8066, USA. ed.castner@rutgers.edu

Annual Review of Physical Chemistry
|November 25, 2010
PubMed
Summary
This summary is machine-generated.

Ionic liquids, salts with low melting points, are being studied for their unique properties. Research is exploring their supramolecular structure, nanoscale ordering, and effects on chemical reactions, with ongoing debates about their influence.

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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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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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From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding

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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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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
06:44

From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding

Published on: March 24, 2018

Area of Science:

  • Physical Chemistry
  • Materials Science

Background:

  • Ionic liquids (ILs) are salts with low melting points, garnering significant research interest.
  • Recent advancements have focused on understanding the factors contributing to their unique properties.

Purpose of the Study:

  • To investigate the role of supramolecular structure and organization in ionic liquids.
  • To explore the impact of ionic liquids on chemical reactions and processes.
  • To address the ongoing debate regarding nanoscale ordering in ionic liquids.

Main Methods:

  • Literature review and synthesis of recent findings in ionic liquid research.
  • Analysis of experimental and theoretical studies on ionic liquid properties.
  • Examination of emerging data on reactivity within ionic liquids.

Main Results:

  • Supramolecular structure and organization are identified as critical factors influencing ionic liquid behavior.
  • Nanoscale ordering in ionic liquids is a complex and actively debated topic.
  • Reactivity in ionic liquids is relatively unexplored but may involve distributed kinetics and dynamical heterogeneity.

Conclusions:

  • Understanding supramolecular organization is key to unlocking the full potential of ionic liquids.
  • Further research is needed to fully elucidate the nature of nanoscale ordering and its implications.
  • The influence of distributed kinetics and dynamical heterogeneity on ionic liquid reactivity requires continued investigation.