| ydrogen bonding is critical in the structure and reactivity of many molecular systems. Symmetric, low-barrier hydrogen bonds have been proposed as essential in the catalytic mechanism of many enzymes. Various experimental techniques have been used over the years to investigate the strength and symmetry of hydrogen bonds. Correlations between hydrogen bond distances from crystal data and isotopic changes on IR and NMR frequencies have been the best sources for judging the symmetry of hydrogen bonds. Nevertheless many of the techniques have limits and the data is inconclusive about the existence or nature of symmetric hydrogen bonds in solution. New methods that can measure directly the symmetry of the hydrogen bond are needed.;The method of isotopic perturbation of equilibrium can distinguish between hydrogens in a single- and a double-well potential. The ;NMR primary isotope shifts were used to determine the symmetry of hydrogen bonds. The monoanions of phthalic, 3,4,5,6-tetrahydrophthalic, 1,2-cyclopentenedicarboxylic, and 3,4-furandicarboxylic acids were examined in organic solvents by... |
