N-Phenyl-maleamic acid

The two independent mol-ecules in the title compound (systematic name: 4-amino-4-oxobut-2-enoic acid), C(10)H(9)NO(3), are both essentially planar (r.m.s. deviations = 0.05 and 0.06 Å). In both mol-ecules, the -OH group forms an intra-molecular hydrogen bond to the amide O atom. Adjacent mol-ecules are linked by N-H⋯O hydrogen bonds into a flat ribbon that runs along the a axis of the monoclinic unit cell.