University of Illinois Urbana-Champaign

Endocyclic restriction test: Determination of a geometrical dependance for an aryl bromide-alkyllithium exchange reaction

Allen, David John

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Description

Title
Endocyclic restriction test: Determination of a geometrical dependance for an aryl bromide-alkyllithium exchange reaction
Author(s)
Allen, David John
Issue Date
1991
Doctoral Committee Chair(s)
Beak, Peter
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Organic
Language
eng
Abstract
  • The geometrical dependance for an aryl bromide-alkyllithium exchange reaction has been investigated by use of the endocyclic restriction test.
  • There have been four mechanistic alternatives presented for the aryl bromide-alkyllithium exchange reaction: a four-centered transition structure mechanism; a single-electron mediated mechanism; an S$\sb{\rm N}$2 attack at bromine; and a pathway involving the formation of a bromine ate complex intermediate. The four-center mechanism proceeds with a small C-Br-C transition structure angle, whereas the S$\sb{\rm N}$2 and ate complex formation mechanisms proceed with a large C-Br-C angle. The single-electron transfer mediated mechanism involves dissociation to give bromide and therefore should not have a geometrical dependance in respect to a C-Br-C transition structure angle.
  • Through double double-label experiments, we have determined that the aryl bromide-alkyllithium exchange of 52 to 53 proceeds intermolecularly in systems in which an intramolecular exchange through a five-, six-, and eight-membered endocyclic ring is available. The exchange will proceed intramolecularly through an eighteen-membered endocyclic ring. This is the first determination of a geometrical dependance for an aryl bromide-alkyllithium exchange.
  • Through these results, we have ruled out the four-center mechanism, which should proceed intramolecularly though the smaller endocyclic ring systems. The observation of a geometrical dependance also rules out the single-electron transfer mechanism. The mechanistic alternatives which involve large C-Br-C transition structure angles, the S$\sb{\rm N}$2 attack at bromine and the bromide ate complex intermediate mechanisms, are supported by our observations.(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI)
Type of Resource
text
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http://hdl.handle.net/2142/22066
Copyright and License Information
Copyright 1991 Allen, David John

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