Conformational Flexibility in N-Benzylideneanilines

Molecules of N-(p-methoxybenzylidene)-m-nitroaniline, C₁₄H₁₂N₂O₃. (I), are essentially planar in the solid state, with average torsion angles of 15.7 (6), -179.6 (4) and -8.3 (6)° respectively about the C-N, N=C and C-C bonds of the central unit joining the two aromatic rings. The crystal packing consists of stacks of identically oriented molecules related by pure translation symmetry, with a perpendicular spacing of 3.490 (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; average torsion angles about C-N, N=C and C-C are 14.7 (2), -178.0 (1) and 1.0 (2)°, respectively, for (IIA) and 40.6 (2), -177.5 (1) and 5.7 (2)°, respectively, for (IIB). Molecules of (IIA) form stacks with an alternating head-to-tail arrangement and spacings of 3.319 (2) and 3.446 (2) Å; molecules of (IIB) also stack head-to-tail with parallel rings 3.277 (2) Å apart.

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