Our research in physical-organic chemistry is concerned with molecular structure, mechanisms of organic reactions, and effects of structure on reactivity. Areas of current activity include development of NMR methods for chemical kinetics and studies of the symmetry of hydrogen bonds, of kinetic isotope effects, of stereochemical effects on reactivity, of the anomeric effect, and of steric hindrance to solvation of ions. The NMR method of isotopic perturbation was used to distinguish between these in monoanions of 18 O-labeled maleic and phthalic acids. These had always been considered as having a symmetric intramolecular hydrogen bond. Nevertheless, the observed 13 C isotope shifts show that they, and many other monoanions of dicarboxylic acids, exist as a pair of tautomers in all solutions, not just in water as we had thought.
Cationic groups seem to prefer the equatorial position on a sugar molecule.
We find that the change that occurs upon N-protonation is small and can be accounted for on the basis of steric effects and an enhancement of the normal anomeric effect. Moreover, on protonating glucosylimidazole, the equilibrium is shifted toward the axial conformer. Therefore, we conclude that the reverse anomeric effect does not exist. We are now able to evaluate the extra energy cost required to place an ionic substituent into the axial position, relative to the energy for the corresponding neutral. The exceptionally high accuracy permits dissection into entropy and enthalpy contributions, according to the temperature dependence.