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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.
Ion Exchange01:17

Ion Exchange

Ion exchange chromatography separates charged molecules from a solution by reversibly exchanging them with mobile, or 'active', ions associated with the oppositely charged stationary phase. This method can be used to separate ions, soften and deionize water, and purify solutions. The polymers comprising the ion-exchange column are high-molecular-weight and chemically stable polymers, crosslinked to be porous and essentially insoluble. They are also functionalized with either acidic or basic...
Ion-Exchange Chromatography01:09

Ion-Exchange Chromatography

Ion-exchange chromatography, or IEC, is a technique for separating ions based on their affinity for the stationary phase. The stationary phase is a cross-linked polymer resin with covalently attached ionic functional groups. The functional groups can be either positively charged (cation exchangers) or negatively charged (anion exchangers). A cation exchanger consists of a polymeric anion and active cations, while an anion exchanger is a polymeric cation with active anions. The choice of...
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 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.
Types of Reversible Electrodes01:24

Types of Reversible Electrodes

For electrode reversibility to be maintained, all the reactants and products involved in the half-reaction must be present at the electrode. There are several types of reversible electrodes (half-cells).In metal-metal-ion electrodes, a metal balances electrochemically with a solution of its own ions. Examples are Cu2+|Cu and Zn2+|Zn. Metals that react with the solvent, like group 1 and most group 2 metals, which react with water, and zinc, which reacts with aqueous acidic solutions, cannot be...

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Merging Ion Concentration Polarization between Juxtaposed Ion Exchange Membranes to Block the Propagation of the Polarization Zone
08:06

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Reversible exciplex formation followed charge separation.

M V Petrova1, A I Burshtein

  • 1International Tomography Center, Novosibirsk 630090, Russia Novosibirsk State University, Novosibirsk 630090, Russia.

The Journal of Physical Chemistry. A
|December 20, 2008
PubMed
Summary
This summary is machine-generated.

This study models exciplex formation, ion pair decomposition, and recombination to singlet and triplet products. It provides quantum yields for excited states and fluorescence under various conditions.

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Area of Science:

  • Photochemistry
  • Chemical Kinetics
  • Physical Chemistry

Background:

  • Exciplex formation and ion pair decomposition are key processes in photochemistry.
  • Understanding geminate and bulk ion recombination is crucial for predicting product yields.

Purpose of the Study:

  • To develop a kinetic model for exciplex formation, ion pair decomposition, and subsequent recombination.
  • To determine quantum yields and product distributions under pulse and stationary excitation.

Main Methods:

  • Derivation of integral kinetic equations for state populations.
  • Modeling spin conversion via incoherent (rate) mechanisms.
  • Incorporating contact electron transfer and heavy particle reactions.

Main Results:

  • Solutions derived for integral equations, expressed via reaction constants and diffusion characteristics.
  • Calculated quantum yields for excited states and exciplex fluorescence.
  • Determined yields of free ions and triplet products under pulse excitation, and stationary concentrations under continuous pumping.

Conclusions:

  • The developed model accurately describes the complex reaction pathways.
  • Provides a framework for predicting photochemical outcomes based on fundamental reaction parameters.