ORGN 99 |
| Isotopic perturbation of degenerate equilibrium is used to determine whether tetramethylethylene iodonium ion is a closed 1,2-bridged structure or an equilibrium of open beta-iodocarbenium ions. An isotopically labeled precursor 2,3-dimethyl-3-fluoro-2-iodo-butane-1,1,1-d3 was reacted with antimony pentafluoride in SO2. The observed 13C NMR chemical shifts are consistent with the production of a closed 1,2-bridged iodonium ion. The difference in the observed isotope shifts for the quaternary carbon signals was 100 ppb. This difference can be rationalized with two- and three-bond intrinsic isotope shifts only; the difference is too small to result from an isotopic perturbation of equilibrium. The observed isotope shifts for the methyl carbon are small and upfield and can also be explained with intrinsic shifts only. Due to the absence of equilibrium isotope shifts, we conclude that this ion is indeed the tetramethylethylene iodonium ion.
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Physical Organic Chemistry, Combinatorial and Process Chemistry, New Reactions and Methodology, Peptides, Proteins and Amino Acids
8:00 PM-10:00 PM, Sunday, April 6, 2008 Morial Convention Center -- Hall A, Poster
Division of Organic Chemistry |
