Two trans-4-aminoazoxybenzenes

Two isomeric trans‐4‐amino­azoxy­benzenes, trans‐1‐(4‐amino­phenyl)‐2‐phenyl­diazene 2‐oxide (α, C12H11N3O) and trans‐2‐(4‐amino­phenyl)‐1‐phenyl­diazene 2‐oxide (β, C12H11N3O), have been characterized by X‐ray diffraction. The α isomer is almost planar, having torsion angles along the Caryl—N bonds of only 4.9 (2) and 8.0 (2)°. The relatively short Caryl—N bond to the non‐oxidized site of the azoxy group [1.401 (2) Å], together with the significant quinoid deformation of the respective phenyl ring, is evidence of conjugation between the aromatic sextet and the π‐electron system of the azoxy group. The geometry of the β isomer is different. The non‐substituted phenyl ring is twisted with respect to the NNO plane by ca 50°, whereas the substituted ring is almost coplanar with the NNO plane. The non‐oxidized N atom in the β isomer has increased sp3 character, which leads to a decrease in the N—N—C bond angle to 116.8 (2)°, in contrast with 120.9 (1)° for the α isomer. The deformation of the C—C—C angles (1–2°) in the phenyl rings at the substitution positions is evidence of the different character of the oxidized and non‐oxidized N atoms of the azoxy group. In the crystal structures, mol­ecules of both isomers are arranged in chains connected by weak N—H⃛O (α and β) and N—H⃛N (β) hydrogen bonds.