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Related Concept Videos

Mass Spectrometry: Molecular Fragmentation Overview01:20

Mass Spectrometry: Molecular Fragmentation Overview

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The ionization of a molecule into a molecular ion inside the mass spectrometer causes instability in the molecule's structure due to the loss of an electron. This eventually leads to the fragmentation or breaking of some bonds in the molecule. The fragmentation occurs predominantly at specific bonds to yield relatively stable fragments.
One type of fragmentation pattern is the cleavage of a single bond in the molecular ion. The cleavage leads to a radical and a cation. The cleavage can occur at...
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[3,3] Sigmatropic Rearrangement of Allyl Vinyl Ethers: Claisen Rearrangement01:24

[3,3] Sigmatropic Rearrangement of Allyl Vinyl Ethers: Claisen Rearrangement

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The Claisen rearrangement is a [3,3] sigmatropic rearrangement of allyl vinyl ethers to unsaturated carbonyl compounds. The rearrangement is a concerted pericyclic reaction proceeding via a chair-like transition state.
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Mass Spectrometry: Alkyne Fragmentation00:53

Mass Spectrometry: Alkyne Fragmentation

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The fragmentation of alkynes preferentially occurs at the carbon–carbon bond between the α and β carbon of the alkyne bond to generate a 3-propynyl cation (or propargyl cation). In terminal alkynes, there is the only type of fragmentation that yields the 3-propynyl cation. The unsubstituted 3-propynyl cation exhibits a peak at a mass-to-charge ratio of 39. In internal alkynes, the 3-propynyl cation is substituted. For example, 2-pentyne fragments into methyl-substituted 3-propynyl cation,...
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Mass Spectrometry: Alkene Fragmentation00:59

Mass Spectrometry: Alkene Fragmentation

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Alkenes lose one electron from the unsaturated π bond upon ionization and form stable molecular ions. Further fragmentation of alkenes occurs through three different reaction pathways. The most prominent fragmentation is the cleavage at the allylic position. The resultant allylic carbocation is resonance stabilized. In the mass spectra of terminal alkenes, this fragment appears at a mass-to-charge ratio of 41. In the internal alkenes, where there are two choices of allylic cleavage, the...
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Ethers to Alkyl Halides: Acidic Cleavage02:18

Ethers to Alkyl Halides: Acidic Cleavage

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Ethers are generally unreactive and unsuitable for direct nucleophilic substitution reactions since the alkoxy groups are strong bases and, therefore, poor leaving groups. However, ethers readily undergo acidic-cleavage reactions. Ethers can be converted to alkyl halides when heated with strong acids such as HBr and HI in a sequence of two substitution reactions.
7.5K
Alkynes to Carboxylic Acids: Oxidative Cleavage02:01

Alkynes to Carboxylic Acids: Oxidative Cleavage

7.1K
Alkynes undergo oxidative cleavage in the presence of oxidizing reagents like potassium permanganate and ozone. The triple bond — one σ bond and two π bonds — is completely cleaved, and the alkyne is oxidized to carboxylic acids. When warm and basic aqueous potassium permanganate is used as an oxidizing agent, alkynes are first converted to carboxylate salts via an unstable α-diketone intermediate. Further, a mild acid treatment protonates the carboxylate anions...
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A Novel Allyl Transfer Coupled with a Grob Fragmentation.

Shao-Gang Li1, Hui-Jun Chen1, Yang-Yang Yang1

  • 1State Key Laboratory of Bioorganic and Natural Products Chemistry, Collaborative Innovation Center of Chemistry for Life Sciences, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Road, Shanghai, 200032, China.

Chemistry, an Asian Journal
|August 29, 2015
PubMed
Summary

A new acid-promoted rearrangement involves allyl group migration and stereoselective Grob fragmentation. This novel transformation is rationalized by a six-membered transition state mechanism, offering insights into organic reaction pathways.

Keywords:
Aldol reactionallylationmigrationpolyketidesrearrangement

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Area of Science:

  • Organic Chemistry
  • Reaction Mechanisms
  • Stereoselective Synthesis

Background:

  • Understanding novel organic transformations is crucial for synthetic chemistry.
  • Acid-promoted reactions and rearrangements are fundamental in organic synthesis.

Purpose of the Study:

  • To disclose a previously unknown acid-promoted rearrangement reaction.
  • To elucidate the mechanism and stereochemical outcome of this novel transformation.

Main Methods:

  • Investigation of an acid-promoted rearrangement using various substrates.
  • Analysis of reaction products to determine stereoselectivity.
  • Hypothesizing a reaction mechanism involving a six-membered transition state.

Main Results:

  • Demonstration of a novel allyl group migration to a carbocation.
  • Observation of stereoselective intramolecular Grob fragmentation.
  • Successful rationalization of rearrangement outcomes with a proposed mechanism.

Conclusions:

  • A new acid-promoted rearrangement pathway has been discovered.
  • The reaction proceeds via a stereoselective Grob fragmentation.
  • A six-membered transition state mechanism explains the observed outcomes.