Symmetries of Hydrogen Bonds in Solution

• Published in: Science (American Association for the Advancement of Science) Vol. 266; no. 5191; pp. 1665 - 1668
• Main Author: Perrin, Charles L.
• Format: Journal Article
• Language: English
• Published: Washington, DC American Society for the Advancement of Science 09-12-1994; American Association for the Advancement of Science; The American Association for the Advancement of Science
• Subjects: Aqueous solutions; Atomic and molecular physics; Atoms; Carboxylic acids; Chemical equilibrium; Crystals; Effects of atomic and molecular interactions on electronic structure; Electronic structure of atoms, molecules and their ions: theory; Environmental and solvent effects; Exact sciences and technology; Hydrogen; Hydrogen bonding; Hydrogen bonds; Isotope effects; Molecular association; Molecular properties and interactions with photons; Nuclear resonance and relaxation; Physics; Protons; Solvents; Anions; Aqueous solutions; Apolar solvent; Dicarboxylic acids; NMR spectrometry; Tautomer; Experimental study; Intramolecular hydrogen bond; Organic compounds
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.266.5191.1665

The nuclear magnetic resonance method of isotopic perturbation can distinguish between single- and double-well potentials in intramolecularly hydrogen-bonded monoanions of dicarboxylic acids. These are classic cases of a "strong," symmetric hydrogen bond in the crystal. The observed carbon-13 isotope shifts induced by the substitution of oxygen-18 demonstrate that these monoanions exist as a single symmetric structure in a nonpolar solvent but as two equilibrating tautomers in aqueous solution. The change is attributed to the disorder of the aqueous environment. These are simple counterexamples to the hope that the crystal structure reveals the actual molecular structure in aqueous solution.