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Isotope effects for fluorine-18 and carbon-11 in the study of reaction mechanisms

✍ Scribed by Olle Matsson; Susanna MacMillar

Publisher
John Wiley and Sons
Year
2007
Tongue
French
Weight
132 KB
Volume
50
Category
Article
ISSN
0022-2135

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✦ Synopsis

Abstract

The use of kinetic isotope effects (KIEs) for the short‐lived radionuclides ^11^C and ^18^F in the study of reaction mechanisms is described using some examples. Leaving group fluorine KIEs (k^18^/k^19^) have been utilized to determine the rate‐limiting step for nucleophilic aromatic substitution reactions (S~N~Ar). The fluorine KIE was also used to probe the effect of changing solvent and nucleophile steric hindrance on rate‐limiting step. The mechanism for a base promoted elimination reaction was determined to be stepwise (E1cB) by a multiple KIE study including the leaving group fluorine KIE. The transition state structures for aliphatic nucleophilic substitution reactions (S~N~2) have been investigated by multiple KIE studies for cases where the substrate substitution, leaving group or solvent has been varied. Carbon KIEs for labelled α‐carbon atom in the substrate are large, k^11^/k^14^ = 1.189–1.220. For labelled nucleophile cyanide ion, k^11^/k^14^ = 0.99951–1.0119. Copyright Β© 2007 John Wiley & Sons, Ltd.

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