The mol­ecule of the title benzohydrazide derivative, C15H14N2O4, exists in a trans conformation with respect to the C=N double bond and is twisted, the dihedral angle between the two benzene rings being 24.17 (6)°. The meth­oxy group is almost co-planar with respect to the attached benzene ring [Cm—O—C—C (m = meth­yl) = −1.45 (17)°]. In the crystal, the mol­ecules are linked by N—H⋯O and O—H⋯O hydrogen bonds into sheets parallel to the bc plane. These sheets are further connected into a three-dimensional network by weak C—H⋯O and C—H⋯π inter­actions.

The title benzohydrazide derivative, C17H18N2O5, exists in a trans conformation with respect to the C=N double bond. The dihedral angle between the benzene rings is 19.41 (5)°. The two meth­oxy groups at the meta positions of the trimeth­oxy­benzene group are almost coplanar with the ring [C—O—C—C = 1.62 (16) and 178.33 (10)°], whereas the third meth­oxy group, at the para position, is (+)-synclinal with the ring. In the crystal, mol­ecules are linked by N—H⋯O and bifurcated O—H⋯(N,O) hydrogen bonds, as well as weak C—H⋯O inter­actions, into sheets lying parallel to the ac plane. A C—H⋯π inter­action also occurs.

The mol­ecule of the title benzohydrazide derivative, C15H14N2O4, is twisted and exists in a trans conformation with respect to the C=N double bond. The dihedral angle between the benzene rings is 56.86 (9)° and the C atom of the meth­oxy group deviates slightly [C—O—C—C = −10.4 (3)°] from its attached benzene ring. An intra­molecular O—H⋯N hydrogen bond generates an S(6) ring. In the crystal, mol­ecules are linked by N—H⋯O and bifurcated N—H⋯(O,O) hydrogen bonds, as well as weak C—H⋯O inter­actions, into two-dimensional networks lying parallel to the bc plane. A weak C—H⋯π inter­action also occurs.

In the title compound, C15H13BrN2O3·H2O, the dihedral angle between the two benzene rings is 13.92 (6)°. The meth­oxy group of the 4-hy­droxy-3-meth­oxy­phenyl is almost coplanar with its bound benzene ring, as seen by the Cmeth­yl—O—C—C torsion angle of −0.35 (16)°. In the crystal, mol­ecules are linked into a three-dimensional network by N—H⋯O, O—H⋯N and O—H⋯O hydrogen bonds and also weak C—H⋯O inter­actions. A short C⋯O contact of 3.0191 (15) Å is also present.

This paper is dedicated to the late His Royal Highness Prince Mahidol of Songkla for his contributions to the development of medical education in Thailand on the occasion of Mahidol Day which falls on the 24th September.