Unusual crystal structure of N-substituted maleamic acid - very strong effect of intramolecular hydrogen bonds.

N-Carbamylmaleamic acid (malur) undergoes cyclodehydration under favourable conditions, as expected, to give N-carbamyl maleimide. N-(Carboxymethyl) maleamic acid (malgly), however, does not undergo a similar cyclization reaction. Strong π bonding between the C and N of the amide group as well as two intramolecular hydrogen bonds makes malgly a planar molecule, as revealed by single-crystal X-ray studies.