Our work on the gas-phase dissociation of benzyl dimethylsulfoniums and pyridiniums, and the computational studies supporting our conclusions, has been completed and the paper describing this work is in press at the Journal of Organic Chemistry. We showed that the ribosyl oxocarbenium ion is intrinsically more stable in the gas phase than the 4-methoxybenzyl carbenium ion, despite the contention that the oxocarbenium ion should be less stable in solution than the benzyl species, which we and others have show to be a solvent-equilibrated species on the reaction coordinate. Work on modeling studies of putative primary ion pairs in antibody-catalyzed cleavage reactions using the facilities of the Computer Graphics Lab, has been completed and has been submitted for publication. In brief, in a highly speculative computation, I showed that the substrate for the Lerner-Janda antibody is stable under normal conditions, but that if it is assumed that protease-like structures exist in the antibody--a speculation in complete accord with Scanlan's recent work--then protonation of the substrate leaving group leads to the products found for the reactions of the antibody. This was extended to a structurally related substrate for the antibody, and the computation very successfully reproduced the known products from two separate clones of the antibody. Work on a long-standing problem involving the stability of cyclopropyl carbinyl carbenium ions generated by protonating the respective ketones in strong acid media has been completed and is being written up. Using simple isodesmic cycles, I was able to show that seemingly anomalous spectral data for a bicyclic system is in fact related to orbital symmetries rather than to intrinsic energies. The energies computed match precisely the various measures of stability, including pKR+ and NMR shift values. Work on the hydration reactions of dialkoxy onium ions has been completed and submitted for publication. The results of transition-state modeling and isodesmic cyclic computations suggest that steric hindrance to solvation of these highly stable oxonium ion species and not a lack of resonance interaction with the reaction center controls the kinetics of hydration. This view is counterintuitive, but the data are fully supportive of it.
Showing the most recent 10 out of 508 publications
