Synthesis and structural characterization of N-methyl-DL-glutamic acid

The solid-state conformation of racemic N-methylglutamic acid has been defined by single-crystal X-ray crystallography. Orthorhombic crystals belong to the space group P bca with a 15.219(2), b 10.583(1), c 9.595(1) Å and Z 8. The structure was refined to a final R value of 0.049 for the 1285 measured data. In the crystal the molecules adopt a zwitterionic form with protonation having occurred at the amino nitrogen atom. The α-carboxyl is unprotonated with the δ-carboxy group retaining a proton. The i.r. spectrum shows absorptions which also are indicative of the amino acid being in the zwitterionic form. Intermolecular H-bonds involving the carboxylate proton and the two protons on the N-atom link the molecules into a three-dimensional network in the crystal.