In the title compound, C10H12O5, the dihedral angle between the benzene ring is almost coplanar with the attached C(O)—O—C group [dihedral angle = 0.32 (15)°]. In the crystal, two intermolecular O—H⋯O hydrogen bonds make R 4 4(26) ring mofits.

In the title compound, C12H14O4, a derivative of caffeic acid [(E)-3-(3,4-dihy­droxy­phen­yl)-2-propenoic acid], an intra­molecular O—H⋯O hydrogen bond forms an S(5) ring. In the crystal, inter­molecular O—H⋯O hydrogen bonds link mol­ecules into chains propagating in [110].

In the crystal structure of the title compound, C10H12O4, O—H⋯O hydrogen bonds incorporating R 2 2(10) and R 2 2(14) motifs link mol­ecules into chains along [10]. An intra­molecular O—H⋯O hydrogen bond is also observed.

The title compound, C12H16O5, is a derivative of β-(3,4-dihydroxy­phen­yl)-α-hydr­oxy acid. The crystal packing is stabilized by inter­molecular O—H⋯O hydrogen bonds.