Investigation of hydrogen-bonded compounds by high-resolution NMR spectroscopy of solids: Part 2. Symmetry and strength of OH … O bonds in some hydrogen-bonded compounds containing carboxylic groups determined by 1H and 13C chemical shifts

Abstract

1H and 13C high-resolution solid-state NMR using magic angle sample spinning is applied to determine the strength and symmetry of the OH … O bonds in the hydrogen-bonded compounds potassium hydrogen malonate (KHM), succinate (KHS) and phthalate (KHPh), ammonium hydrogen glutarate (AHG) and its deuterated analogue (ADG), the cis-trans isomers ammonium hydrogen maleate (AHM) and fumarate (AHF) and maleic and fumaric acids. A marked loss of symmetry of the H-bond is observed in ADG relative to AHG. The R O…O distances and symmetry are estimated for AHM and AHF. In general, the 1H chemical-shift values, σ , yield information on the strength of the H-bonds while conclusions concerning the symmetry of the H-bonding may be deduced from the 13C σ values which are sensitive to crystallographic and molecular symmetry. These key signals in the case of strongly H-bonded carboxylic groups are sufficiently distinct from other signals as to yield reliable information on the type of H-bond. This information can now be obtained from NMR investigations of polycrystalline samples at room temperature.