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Beak, Peter Allen, David John 2011-05-07T13:27:52Z 2011-05-07T13:27:52Z 10000-01-01 1991 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) Made available in DSpace on 2011-05-07T13:27:52Z (GMT). No. of bitstreams: 2 license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5) 9136527.pdf: 6087651 bytes, checksum: 86f36a5cc2457af4d026bcab97f5cdb7 (MD5) Previous issue date: 1991 Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding (hding2@illinois.edu) on 2011-05-07T14:55:05Z Item is restricted indefinitely. Restriction data tranferred 2014-07-01T11:25:39-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: ETDs are only available to UIUC Users without author permission ETDs are only available to UIUC Users without author permission U of I Only AAI9136527 (UMI)AAI9136527 http://hdl.handle.net/2142/22066 eng Copyright 1991 Allen, David John Chemistry, Organic Endocyclic restriction test: Determination of a geometrical dependance for an aryl bromide-alkyllithium exchange reaction text Chemistry Chemistry University of Illinois at Urbana-Champaign Dissertation Ph.D.