In the title compound, C(10)H(12)O(5), 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 crystal structure of the title compound, C(10)H(12)O(4), O-H⋯O hydrogen bonds incorporating R(2) (2)(10) and R(2) (2)(14) motifs link mol-ecules into chains along [1[Formula: see text]0]. An intra-molecular O-H⋯O hydrogen bond is also observed.
The title compound, C(12)H(16)O(5), is a derivative of β-(3,4-dihydroxy-phen-yl)-α-hydr-oxy acid. The crystal packing is stabilized by inter-molecular O-H⋯O hydrogen bonds.
In the title compound, C(12)H(14)O(4), a derivative of caffeic acid [(E)-3-(3,4-dihy-droxy-phen-yl)-2-propenoic acid], an intra-molecular O-H⋯O hydrogen bond forms an S(5) ring. In the crystal, inter-molecular O-H⋯O hydrogen bonds link mol-ecules into chains propagating in .