Hydrogen bonding in C-methylated nitroanilines: three triclinic examples with Z′ = 2 or 4

4-Methyl-2-nitro­aniline, (I), C₇H₈N₂O₂, crystallizes with two mol­ecules in the asymmetric unit. The mol­ecules both form intramolecular N—H⃛O hydrogen bonds and they are linked into hydrogen-bonded C₂²(12) chains in which the two independent mol­ecules alternate. 4,5-Di­methyl-2-nitro­aniline, (II), C₈H₁₀N₂O₂, also has Z′ = 2 and the two independent mol­ecules each form hydrogen-bonded C(6) chains. In 4-­methyl-3-nitro­aniline, (III), C₇H₈N₂O₂, there are four mol­ecules in the asymmetric unit. Molecules of two of these types are linked by N—H⃛O hydrogen bonds into molecular ladders containing R₄³(18) rings and the other two types independently form single C(7) chains.