ORGN 88 |
| Chloronium ions are intermediates in electrophilic chlorine additions to alkenes. Their structure is usually represented as a symmetric static structure having equal C-Cl bond orders. However, these intermediates may exist as a pair of rapidly equilibrating isomers with disparate C-Cl bond orders. To discriminate between these two structures isotopic perturbation of equilibrium, an NMR method used to detect the presence of rapid equilibria, was applied to tetramethylethylene and tetramethylene chloronium ions. The 13C NMR spectra of the labeled and unlabeled compounds were compared to measure the magnitude and direction of the chemical shift differences due to the presence of the isotopes. Results indicate the presence of intrinsic isotope shifts only. Additionally, the equilibrium isotope shifts for these ions were estimated using computationally derived vibrational frequencies and NMR chemical shifts. The potential energy surfaces of these compounds were characterized at the HF, DFT, and MP2 levels of theory with Pople-style basis sets. Experimental NMR data and theoretical calculations support the hypothesis that these chloronium ions are symmetric, with equal C-Cl bond orders. |
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Process R&D, Physical Organic Chemistry, Heterocycles, Aromatics, Metal-Mediated Reactions
8:00 PM-10:00 PM, Sunday, March 25, 2007 Hyatt Regency Chicago -- Riverside Center, Poster
Sci-Mix
Division of Organic Chemistry |