ORGN 448 |
| The structure of bromonium ions will be studied by isotopic perturbation of equilibrium. We wish to address whether the bromonium ion exists as a single symmetric structure with equal C-Br bond orders (1) or as a rapid equilibrium of isomers with unequal C-Br bond orders (2). If the equilibrium is fast relative to the NMR timescale, a standard NMR spectrum will not distinguish between the two structures. However, they can be distinguished with isotopic perturbation of equilibrium, an NMR method used to detect the presence of a rapid equilibrium. As its name suggests, the method uses isotopes to perturb the equilibrium, should an equilibrium exist. This altered equilibrium will cause dynamically related carbons to have different time-averaged NMR chemical shifts relative to the non-deuterated, parent compound. Theory predicts that a downfield shift for a deuterated compound indicates the presence of equilibrium. The method will require the synthesis of 1,5-dibromo-1,1-dideuteropentane (3), 2,3-dibromo-1,1,1-trideutero-3-methyl-2-trideuteromethyl butane (4), and 1,4-dibromo-1-methyl-4-trideuteromethyl cyclohexane (5). Under superacidic conditions at low temperatures, these compounds generate bromonium ions that can be characterized by NMR.
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New Reactions, Methodology, Total Synthesis, Physical Organic Chemistry
8:00 PM-10:00 PM, Tuesday, 15 March 2005 Convention Center -- Sails Pavilion, Poster
Sci-Mix
Division of Organic Chemistry |
