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Is the McLafferty rearrangement of ketones concerted or stepwise? The application of kinetic isotope effects

✍ Scribed by Michael B. Stringer; Dennis J. Underwood; John H. Bowie; Colin E. Allison; Kevin F. Donchi; Peter J. Derrick

Book ID: 102966439
Publisher: John Wiley and Sons
Year: 1992
Tongue: English
Weight: 767 KB
Volume: 27
Category: Article
ISSN: 1076-5174
DOI: 10.1002/oms.1210270319

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✦ Synopsis

Intramolecular I3C and 'H isotope effects have been measured for unimolecular losses of ethene (the McLafferty rearrangement) from metastable molecular ions of 2-ethyI-l-phenylbutan-l-one, kthylpentan-Zone and heptan-4one. Primary and secondary deuterium isotope effects are observed at the y-(terminal) and fl-positions, respectively. Large primary isotope effects occur at fl-positions and for the y positions of 3-ethylpentan-2-one and heptan-4one. The carbon isotope effects in the cases of the doubly isotopically labelled CH, COCH(C,H,)(13CH,CH,) andCD,COCD(C,L),)('3CD,CD,) are 1.17 (AO.01) and 1.04 (+0.01), respectively. All of these isotope effects are consistent with a stepwise mechanism in which more than one step is rate determining.

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