Intramolecular hydrogen bonding in acid malonates. Infrared, NMR and ab initio MO investigations

On Low-Barrier Hydrogen Bonds and Enzyme Catalysis

“…This point is confirmed by calculations by Kidric et al. (21) and by a more quantitative ab initio free energy perturbation study (Fig. 1 (Fig.…”

NMR Study of Conformational Exchange and Double-Well Proton Potential in Intramolecular Hydrogen Bonds in Monoanions of Succinic Acid and Derivatives

“…For example, the bridging-proton chemical shift of hydrogen malonate dissolved in DMSO covers an unusually broad range of 9À20 ppm, depending on the countercation, indicating a strong influence of the latter on the H-bond geometry and symmetry. 10 Another example is hydrogen maleate dissolved in aprotic solvents, where the primary H/D isotope effects on chemical shifts are evidence for a single The Journal of Physical Chemistry A ARTICLE central proton position, 11 whereas secondary 16 O/ 18 O isotope effects on carboxylic carbon chemical shifts seem to indicate a tautomeric proton exchange between two asymmetric structures. 1,2 The proton position in the hydrogen bridge correlates strongly with the heavy-atom distance: neutron diffraction studies have shown that the central proton positions coincide with shortest heavy-atom distances.…”

“…For example, neutron scattering experiments revealed a central proton position in the case of a symmetric placement of the counterion (K + ) in hydrogen maleate and an asymmetric proton position in the case of an asymmetric location of K + for hydrogen phthalate . In aprotic solvents such as dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), CD 3 CN, and CD 2 Cl 2 , the intramolecular hydrogen bond is usually retained, as indicated by the low-field 1 H NMR chemical shift of the bridging proton. ,− However, the symmetry of the hydrogen bond in liquid solutions is more ambiguous, first, because experimental evidence is usually of indirect spectroscopic nature and, second, because the mobility of the surrounding solvent molecules creates an instantaneous asymmetry of the environment that makes the equilibrium position of the proton time-dependent. For example, the bridging-proton chemical shift of hydrogen malonate dissolved in DMSO covers an unusually broad range of 9–20 ppm, depending on the countercation, indicating a strong influence of the latter on the H-bond geometry and symmetry .…”

Influence of solvent on intramolecular proton transfer in hydrogen malonate: molecular dynamics simulation study of tunneling by density matrix evolution and nonequilibrium solvation

“…5 Although HM does indeed appear in this form in some salts in the solid state (ref 6 and references therein), the Raman spectroscopic data of Maury and Bardet did not confirm the existence of intramolecular hydrogen bonding in aqueous solution.7 However, differences in 13C chemical shifts of the methylene carbon of malonic acid with progressive neutralization were interpreted in terms of intramolecular H-bonding in HM. 8 In solution, one expects an equilibrium between the planar E-conformer, which is characterized by an intramolecular hydrogen bond, and the open Z-conformer. We restrict our considerations to the E-conformer and do not consider the general problem of proton transfer including reaction paths that involve solvent molecules.…”