Conformational flexibility in N-benzylideneanilines

Mols. of N-(p-methoxybenzylidene)-m-nitroaniline, C14H12N2O3, (I), are essentially planar in the solid state, with av. torsion angles of 15.7(6), -179.6(4) and -8.3(6)° about the C-N, N=C and C-C bonds, resp., of the central unit joining the two arom. rings. The crystal packing consists of stacks of identically oriented mols. related by pure translation symmetry, with a perpendicular spacing of 2.490(2) Å. Two different conformations (A and B) of the positional isomer N-(p-methoxybenzylidene)-p-nitroaniline, C14H12N2O3, (II), exist together in the solid state, one much more planar than the other; av. torsion angles about C-N, N=C and C-C are 14.7(2), -178.0(1) and 1.0(2)°, resp., for (IIA), and 40.6(2), -177.5(1) and 5.7(2)°, resp., for (IIB). Mols. of (IIA) form stacks with an alternating head-to-tail arrangement and spacings of 3.319(2) and 3.446(2) Å; mols. of (IIB) also stack head-to-tail with parallel rings 3.277(2) Å apart. Crystallog. data and at. coordinates are given. [on SciFinder(R)]