Solution conformational preferences of glutaric, 3-hydroxyglutaric, 3-methylglutaric acid, and their mono- and dianions

Conformational preferences of glutaric, 3-hydroxyglutaric and 3-methylglutaric acid, and their mono- and dianions have been investigated with the aid of NMR spectroscopy. In contrast to succinic acid, glutaric acid displays essentially statistical conformational equilibria in polar and non-polar solutions of high and low hydrogen-bonding ability with no clear evidence for intramolecular hydrogen-bonding interactions. The acid ionization constant ratios, K_1/K_2, in D_2O and DMSO of glutaric, 3-hydroxyglutaric, and 3-methylglutaric acids also indicate that intramolecular interactions are much less important than, or indeed insignificant, for shorter-chain acids. FTIR studies on 3-methylglutaric acid indicate some preference for either association with solvent or dimerization, depending on the solvent, rather than intramolecular hydrogen bonding