Jeffrey P. Kiplinger

Gas-phase ion-molecule chemistry of borate and boronate esters.

Borate esters B(OR)3 and boronate esters RB(OR)2 undergo ion-molecule reactions to yield both addition products (by an implied radiative emission mechanism), ligand exchange, and proton transfer products, in both positive and negative ion modes. Although an acidity for CH3B(OR)2 could not be determined, HOB(OR)2 has an acidity between acetaldehyde and nitromethane. In light of the negligible polar electron acceptor properties of the -B(OR)2 group, that functionality must therefore be one of the best resonance electron acceptor groups known, almost half again as effective as the nitro group.

Structures of gas-phase C2F 7 (+) ions.

In an ion cyclotron resonance spectrometer, less than 96% of the C7F7+ cation formed on electron ionization of perfluorotoluene reacts with hexamethyldisilazane. In contrast, the C7F7+ from perfluoronorbornadiene or perfluorobicyclo[3.2.O]hepta-2,6-diene is nonreactive with hexamethyldisilazane. Collision-induced dissociation results support this dichotomy, although the evidence is not as clear-cut. The reactive ion is assigned the benzyl structure and the nonreactive ion the tropyl structure, on the basis of analogy with the protio cases. By AM1 calculations, the perfluorobenzyl ion is 25 kcal/mol more stable than the perfluorotropyl ion, the opposite of the situation for the protio analogs (− 12 kcal/mol). Ab initio calculations at the 3–21G level agree with the semiempirical energy difference to within 0.4 kcal/mol; at the more appropriate 6–31G*/MP2 level, the perfluorobenzyl cation is 9.7 kcal/mol more stable than the perfluorotropyl cation.