In the title compound, C(12)H(12)N(2)O, the dihedral angle between the planes of the pyridine and phenyl rings plane is 35.94 (12)°. In the crystal structure, centrosymmetrically related mol-ecules are linked by a pair of N-H⋯N hydrogen bonds, forming a dimer with an R(2) (2)(8) ring motif. In addition, there is an intra-molecular N-H⋯O inter-action.

In the title mol-ecule, C6H8N2, the endocyclic angles are in the range 118.43 (9)-122.65 (10)°. The mol-ecular skeleton is planar (r.m.s. deviation = 0.007 Å). One of the two amino H atoms is involved in an N-H⋯N hydrogen bond, forming an inversion dimer, while the other amino H atom participates in N-H⋯π inter-actions between the dimers, forming layers parallel to (100).

The title compound, C(7)H(10)N(2)O, crystallizes with two independent mol-ecules in the asymmetric unit. The bond lengths and angles in the mol-ecules are within normal ranges. The crystal structure is stabilized by inter-molecular N-H⋯N hydrogen bonds, linking the two independent mol-ecules into hydrogen-bonded dimers.

In the title pyrimidine derivative, C(4)H(4)ClN(3), the 2-chloro and 4-amino substituents almost lie in the mean plane of the pyrimidine ring, with deviations of 0.003 (1) Å for the Cl atom, and 0.020 (1) Å for the N atom. In the crystal, molecules are linked via pairs of N-H⋯N hydrogen bonds, forming inversion dimers. These dimers are further linked via N-H⋯N hydrogen bonds, forming an undulat...

The complete mol-ecule of the title compound, C(4)H(3)ClN(3), is generated by crystallographic mirror symmetry, with the Cl atom, one N atom and two C atoms lying on the reflecting plane. In the crystal structure, inter-molecular N-H⋯N hydrogen bonds link the mol-ecules into chains propagating in [100].