Stabilization of a high energy molecular conformation by specific intermolecular forces, a novel planar benzylideneaniline system

The system containing six benzylideneanilines (BA) has been studied: Group 1:

I:	N-(p-Chlorobenzylideneaniline)m-chloroaniline (BA, X=4-Cl, Y=3-Cl)
II:	N-(p-Bromobenzylideneaniline)m-bromoaniline (BA, X=4-Br, Y=3-Br)
III:	N-(p-Bromobenzylideneaniline)m-chloroaniline (BA, X=4-Br, Y=3-Cl)
IV:	N-(p-Chlorobenzylideneaniline)m-bromoaniline (BA, X=4-Cl, Y=3-Br) Group 2:
V:	N-(m-Chlorobenzylideneaniline)p-bromoaniline (BA, X=3-Cl, Y=4-Br)
VI:	N-(m-Bromobenzylidencaniline)p-chloroaniline (BA, X=3-Br, Y=4-Br)

The crystal structures of Group 1 are isostructural. They crystallize in a monoclinic cell, space groupP2₁. They are rare examples of planar benzylideneanilines in a nondisordered crystal structure. The crystal structures exhibit an intermolecular ring containing five atoms and hal- - - hal. C-H- - - hal interactions, which may contribute to the planarity of the molecule. The structures in Group 2 crystallize in a monoclinic cell, space groupP2₁/c. The conformation is nonplanar and there are no intermolecular halogen- - -halogen interactions. The abovementioned five atom pattern ring does not occur in these structures. These two groups of structures show that the type and mode of molecular substitution can lead to specific intermolecular interactions which in turn stabilize an otherwise unfavorable molecular conformation.