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Related Concept Videos

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.
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.
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
[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement01:21

[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement

The Cope rearrangement is classified as a [3,3] sigmatropic shift in 1,5-dienes, leading to a more stable, isomeric 1,5-diene. The reaction involves a concerted movement of six electrons, four from two π bonds and two from a σ bond, via an energetically favorable chair-like transition state.
Radical Reactivity: Intramolecular vs Intermolecular01:33

Radical Reactivity: Intramolecular vs Intermolecular

Radical reactions can occur either intermolecularly or intramolecularly. In an intermolecular radical reaction, a nucleophilic radical adds to an electrophilic alkene or vice versa. In such reactions, the radical and generally the alkene, which is also called the radical trap, are two different molecules. Additionally, for such intermolecular reactions to occur, the radical trap must be active, present in an excess concentration, and the radical starting material must have a weak carbon–halogen...
Preparation of Epoxides03:00

Preparation of Epoxides

Overview
Epoxides result from alkene oxidation, which can be achieved by a) air, b) peroxy acids, c) hypochlorous acids, and d) halohydrin cyclization.
Epoxidation with Peroxy Acids
Epoxidation of alkenes via oxidation with peroxy acids involves the conversion of a carbon–carbon double bond to an epoxide using the oxidizing agent meta-chloroperoxybenzoic acid, commonly known as MCPBA. Since the O–O bond of peroxy acids is very weak, the addition of electrophilic oxygen of peroxy acids to...

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Isotopic Effect in Double Proton Transfer Process of Porphycene Investigated by Enhanced QM/MM Method
05:51

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Reversible electron-induced cis-trans isomerization mediated by intermolecular interactions.

Ch Lotze1, Y Luo, M Corso

  • 1Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany.

Journal of Physics. Condensed Matter : an Institute of Physics Journal
|September 12, 2012
PubMed
Summary

Researchers demonstrate a novel method to stabilize non-planar organic molecular switches on metal surfaces. This breakthrough enables reversible switching between trans and cis states using scanning tunneling microscopy, overcoming previous energy barriers.

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Area of Science:

  • Surface science
  • Organic electronics
  • Molecular switches

Background:

  • Reversible isomerization of organic molecular switches on metal surfaces is challenging due to energy differences between isomers.
  • Planar conformers typically exhibit higher adsorption energies, hindering non-planar isomer stabilization.

Purpose of the Study:

  • To develop a strategy for stabilizing non-planar isomers of organic molecular switches on metal surfaces.
  • To achieve reversible isomerization using external stimuli.

Main Methods:

  • Adsorption of an imine derivative on a metal surface.
  • Utilizing intermolecular bonding to stabilize the non-planar isomer.
  • Employing scanning tunneling microscopy (STM) for inducing isomerization.
  • Performing model force-field calculations.

Main Results:

  • A strategy was successfully implemented to stabilize a non-planar isomer through intermolecular bonding.
  • Reversible switching between trans and cis-like states was induced using tunneling electrons from an STM.
  • Model force-field calculations indicated electrostatic interactions with neighboring molecules enhance the stability of the cis state.

Conclusions:

  • Intermolecular bonding can stabilize non-planar isomers of organic molecular switches on metal surfaces.
  • STM-induced tunneling electrons provide a viable method for reversible isomerization.
  • Electrostatic interactions play a crucial role in the enhanced stability of specific molecular configurations.