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Related Concept Videos

Radical Reactivity: Overview01:11

Radical Reactivity: Overview

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Radicals, the highly reactive species, gain stability by undergoing three different reactions. The first reaction involves a radical-radical coupling, in which a radical combines with another radical, forming a spin‐paired molecule. The second reaction is between a radical and a spin‐paired molecule, generating a new radical and a new spin‐paired molecule. The third reaction is radical decomposition in a unimolecular reaction, forming a new radical and a spin‐paired...
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Radical Reactivity: Steric Effects01:10

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The presence of electron-donating, electron-withdrawing, or conjugating groups adjacent to a radical center, imparts electronic stabilization to the radicals. Examples of such electronically-stabilized radicals are triphenylmethyl, tetramethylpiperidine‐N‐oxide, and 2,2‐diphenyl‐1‐picrylhydrazyl. These radicals are remarkably stable and are known as persistent radicals. Some of the persistent radicals can even be isolated and purified.
Along with electronic...
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Radical Reactivity: Nucleophilic Radicals01:16

Radical Reactivity: Nucleophilic Radicals

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Radicals adjacent to electron-donating groups are called nucleophilic radicals. These radicals readily react with electrophilic alkenes. The SOMO–LUMO interactions are the driving force for the reaction, where the high-energy SOMO of the electron-rich, nucleophilic radicals interacts with the low-energy LUMO of the electron-deficient, electrophilic alkenes. Such SOMO–LUMO interactions are the basis of reactive radical traps, affecting the selectivity in radical reactions. For...
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Radical Reactivity: Concentration Effects01:20

Radical Reactivity: Concentration Effects

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In a radical reaction, the concentration of starting materials governs the selectivity of a radical. For example, the reaction between an alkyl halide and an alkene, in the presence of tin hydride and AIBN, begins with the generation of a tin radical. The generated radical then abstracts halogen from the alkyl halide, producing an alkyl radical. This alkyl radical can either react with tin hydride, yielding an alkane, or add to an alkene, generating a nitrile-stabilized radical, eventually...
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Radical Reactivity: Intramolecular vs Intermolecular01:33

Radical Reactivity: Intramolecular vs Intermolecular

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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...
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Radical Reactivity: Electrophilic Radicals01:02

Radical Reactivity: Electrophilic Radicals

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Radicals adjacent to electron‐withdrawing groups are called electrophilic radicals. These radicals readily react with nucleophilic alkenes. For example, the malonate radical, in which the radical center is flanked by two electron‐withdrawing groups, reacts readily with butyl vinyl ether, which consists of an electron‐donating oxygen substituent. The reaction between electrophilic malonate radical and nucleophilic vinyl ether is favored because the radical has a...
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Atom Transfer Radical Polymerization of Functionalized Vinyl Monomers Using Perylene as a Visible Light Photocatalyst
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A mechanochemical switch to control radical intermediates.

Elizabeth Brunk1, Whitney F Kellett, Nigel G J Richards

  • 1Laboratory of Computational Chemistry and Biochemistry, EPFL , Lausanne, Switzerland 1015.

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|May 22, 2014
PubMed
Summary
This summary is machine-generated.

Vitamin B₁₂-dependent enzymes use radical chemistry for challenging reactions. A novel mechanochemical switch controls reactive intermediates, ensuring precise enzyme selectivity.

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Area of Science:

  • Biochemistry
  • Enzymology
  • Computational Chemistry

Background:

  • Vitamin B₁₂-dependent enzymes catalyze difficult reactions using radical intermediates.
  • Controlling highly reactive species is crucial for enzyme function and preventing side reactions.

Purpose of the Study:

  • To elucidate the catalytic mechanism of a B₁₂-dependent enzyme.
  • To detail the function of a proposed mechanochemical switch in controlling radical intermediates.

Main Methods:

  • Hybrid quantum mechanical/molecular mechanical (QM/MM) simulations.
  • Analysis of the full catalytic cycle of the enzyme.

Main Results:

  • The enzyme utilizes a mechanochemical switch to stabilize the 5 -deoxyadenosyl radical.
  • The switch releases internal strain when "off" and imposes a distinct conformation when "on" to prevent radical transfer.
  • This mechanism ensures high selectivity in challenging enzymatic reactions.

Conclusions:

  • Enzymes employ sophisticated control strategies, like mechanochemical switches, to manage reactive radical species.
  • The identified switch is key to the selectivity of B₁₂-dependent enzymes in catalyzing thermodynamically unfavorable reactions.