A mediated hydrogen bond in an alpha-hydroxycarboxyl group: X-ray structure of (R,R)-N-methyltartramic acid monohydrate and an ab initio study of model systems

The crystal structure of (R,R)-N-methyltartramic acid monohydrate is presen ted and compared with that of the parent compound, (R,R)-tartaric acid. Des pite some conformational differences between the two molecules the packing is very similar, as it is dictated by the carboxyl rather than the amide fu nction. Particular attention is paid to a mediated three-centre hydrogen bo nd as one of the packing motifs involving the alpha-hydroxycarboxyl moiety. The stability and geometry of such structures in the gas phase and in solu tion are examined via theoretical ab initio methods using the RHF/6-311++G* * and RHF/6-311++G**/Onsager models, respectively. Liquid media, in particu lar those of high polarity, are found to stabilize the structures considera bly.