In the title mol­ecule, C16H25NO4, the non-H atoms, except for the two tert-butyl groups, are roughly planar (r.m.s. deviation of the non-H atoms = 0.086 Å). In the crystal, mol­ecules are linked into inversion dimers by pairs of N—H⋯O hydrogen bonds, forming R 2 2(10) ring motifs.

In the title mol­ecule, C13H19NO4, except for two C atoms of the tert-butyl group, the non-H atoms are almost coplanar (r.m.s. deviation = 0.2542 Å). In the crystal, mol­ecules are linked into centrosymmetric dimers by two inter­molecular N—H⋯O hydrogen bonds, forming an R 2 2(10) ring motif.

In the title mol­ecule, C8H11NO2, the r.m.s. deviation of non-H atoms from their best plane is 0.031 Å. Mol­ecules are connected via a pair of N—H⋯O hydrogen bonds into a centrosymmetric dimer.

In the title compound, C16H18N4O3·2H2O, the dihedral angle between the pyrrole and pyridine rings in the hydrazone mol­ecule is 7.12 (3)°. In the crystal structure, inter­molecular N—H⋯O, O—H⋯N and O—H⋯O hydrogen bonds link the hydrazone and water mol­ecules into double layers parallel to (101). The crystal packing exhibits weak π–π inter­actions between the pyrrole and pyridine rings of neighbouring hydrazone mol­ecules [centroid–centroid distance = 3.777 (3) Å]. The crystal studied was a non-merohedral twin, the refined ratio of twin domains being 0.73 (3):0.27 (3).

The asymmetric unit of the title compound, C38H37N7O2, contains one half-mol­ecule, situated on a twofold rotational axis, in which one amino group is involved in intra­molecular N—H⋯O hydrogen bond and the two phenyl rings are twisted from the plane of pyrazolone ring by 26.69 (10) and 79.64 (8)°. The crystal packing exhibits no classical inter­molecular contacts.