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The structure of the title compound, C9H11NO2, (I), comprises a flat mol­ecule arranged, head‐to‐tail, in linear ribbon arrays via a N—H⋯O=C association. These ribbons end‐on form a herring‐bone structure interconnected via N—H⋯N association. The structure was first determined in 1987 [Sinha & Pattabhi (1987). Proc. Indian Acad. Sci. Chem. Sci. 98, 229–234] in the orthorhombic space group P212121, with R = 0.120, whereas similar cell dimensions and an increased β angle in the present study resulted in monoclinic space group P21/c, with R = 0.065.

Catalytic reduction of 2‐nitrofurans 2 gives low yields of 2‐aminofurans 1 which are not isolated but are trapped using ethyl ethoxymethylenecyanoacetate (6) or ethoxymethylenemalononitrile (7). In these reactions 2‐aminofuran (1a) behaves like a dieneamine with substitution occurring at position 5 of the ring. When the 5‐position is substituted reaction takes place at position 3 and thermal cyclisation of the product gives furo‐[2,3‐b]pyridine derivatives 16. An AM1 calculation of the properties of 2‐aminofuran (1a) is reported and the results are consistent with observed properties.

The structure of the title compound, C9H8N4, comprises non-planar molecules that associate via pyrimidine N--H...N dimer R2(2)(8) hydrogen-bonding associations [N...N 3.1870 (17) A] and form linear hydrogen-bonded chains via a pyrimidine N--H...N(pyridyl) interaction [N...N 3.0295 (19) A]. The dihedral angle between the two rings is 24.57 (5) degrees. The structure of the 1:1 adduct with 4-aminobenzoic acid, C9H8N4*C7H7NO2, exhibits a hydrogen-bonding network involving COOH...N(pyridyl) [O...N 2.6406 (17) A], pyrimidine N--H...N [N...N 3.0737 (19) and 3.1755 (18) A] and acid N--H...O interactions [N...O 3.0609 (17) and 2.981 (2) A]. The dihedral angle between the two linked rings of the base is 38.49 (6) degrees and the carboxylic acid group binds to the stronger base group in contrast to the (less basic) complementary hydrogen-bonding site.

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The structure of the title compound, C10H12N2O5, has been determined and is found to have an intramolecular hydrogen bond between the phenol group and one of the 6‐nitro O atoms. The mol­ecule packs in a zigzag hydrogen‐bonded chain, consisting of an intermolecular hydrogen bond, parallel to the c axis, between the phenol group and a 4‐nitro O atom. The dihedral angle between adjacent molecules in the chain is 82 (3)°.