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Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration02:34

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Carbocations

Carbocations are one of the reaction intermediates formed during several nucleophilic substitutions or elimination reactions. A carbocation is an electron-deficient species with the central carbon atom having six electrons and three bonded atoms. The central carbon in a carbocation is sp2 hybridized with trigonal planar geometry. It has an empty p orbital perpendicular to the plane of the structure that can accept electrons. Thus, carbocations act as strong electrophiles and may react with any...
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Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
10:44

Isolating Free Carbenes, their Mixed Dimers and Organic Radicals

Published on: April 19, 2019

Ultrafast carbene-carbene isomerization.

Jin Wang1, Gotard Burdzinski, Jacek Kubicki

  • 1Department of Chemistry, Ohio State University, Columbus, Ohio 43210, USA.

Journal of the American Chemical Society
|March 28, 2008
PubMed
Summary
This summary is machine-generated.

Photochemistry of aryl diazo ketones was studied. Excited states rapidly decompose via multiple pathways, including Wolff rearrangement and carbene formation, revealing complex reaction dynamics.

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Area of Science:

  • Photochemistry
  • Organic Chemistry
  • Spectroscopy

Background:

  • Aryl diazo ketones are versatile synthetic intermediates.
  • Understanding their excited-state dynamics is crucial for controlling reaction outcomes.

Purpose of the Study:

  • To investigate the ultrafast photochemistry of two isomeric aryl diazo ketones.
  • To elucidate the competing decomposition pathways of excited diazo ketone states.

Main Methods:

  • Femtosecond (fs) time-resolved UV-vis spectroscopy
  • Femtosecond (fs) time-resolved IR spectroscopy

Main Results:

  • Excited states of both isomers decompose in under 300 fs.
  • Multiple decomposition pathways were identified, including concerted Wolff rearrangement and nitrogen extrusion.
  • Specific rotomers exhibit distinct pathways, such as oxygen migration or direct carbene formation.
  • Unrearranged carbene intermediates were observed to isomerize within picoseconds (ps).

Conclusions:

  • The photochemistry of aryl diazo ketones is highly complex and ultrafast.
  • Reaction pathways are sensitive to stereochemistry (rotomer configuration).
  • These findings provide critical insights into carbene formation and rearrangement mechanisms.