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 presented and compared with that of the parent compound, (R,R)-tartaric acid. Despite some conformational differences between the two molecules the packing is very similar, as it is dictated by the carboxyl rather than the amide function. Particular attention is paid to a mediated three-centre hydrogen bond as one of the packing motifs involving the alpha-hydroxycarboxyl moiety. The stability and geometry of such structures in the gas phase and in solution are examined via theoretical ab initio methods using the RHF/6-311++G** and RHF/6-311++G**/Onsager models, respectively. Liquid media, in particular those of high polarity, are found to stabilize the structures considerably.
Department of Crystallography, Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland. urszula@krystal.amu.edu.pl
U
Rychlewska
A
Szarecka
J
Rychlewski
R
Motala