Gas phase hydrogen/deuterium exchange reactions of fluorophenyl anions |
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| Authors: | Shuji Kato Charles H DePuy Scott Gronert Veronica M Bierbaum |
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| Institution: | (1) Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309, USA;(2) JILA, University of Colorado and the National Institute of Standards and Technology, Boulder, CO 80309, USA; |
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| Abstract: | Hydrogen/deuterium (H/D) exchange reactions of fluorophenyl and difluorophenyl anions (C6H4F?, o-C6H3F2?, m-C6H3F2?, p-C6H3F2?) have been studied using the flowing afterglow-selected ion flow tube technique. The C6H4F? anion exchanges all hydrogens for deuterium upon reaction with D2O. The difluorophenyl anions o-, m-, and p-C6H3F2? exchange three, two, and one hydrogen, respectively, with D2O, whereas they undergo one, two, and three H/D exchanges, respectively, with CH3OD. The structures of the anions and the isotope exchange dynamics within the intermediate ion–dipole complexes are discussed using ab initio molecular orbital calculations. Calculated values for the proton affinities of the most stable anions are 385.2, 378.0, 371.9, and 378.2 kcal/mol for C6H4F?, o-C6H3F2?, m-C6H3F2?, and p-C6H3F2?, respectively, in excellent agreement (within 2 kcal/mol) with the previous experimental values for the acidities of the corresponding fluorobenzenes. The H/D exchange results are explained by the energy differences of the intermediate DO? and CH3O? species within the ion–dipole complexes; CH3O? is mobile within the “hot” intermediate complex, whereas DO? is nearly “frozen” within the complex and cannot migrate across the barriers caused by the fluorine atoms or by the π electrons. |
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