Modification of crystal packing and molecular conformation via systematic substitution

Variations in molecular conformation and crystal picking are investigated by systematically altering the subsiitutents on a molecule which has two degrees of conformational freedom. The crystal structures of the heterodisubstituted benzylideneanilines (BA's),p-chloro-N-(p-bromo-benzylidene) aniline (BrCl) and p-bromo-N-(p-chlorobenzylidene) aniline (ClBr) have been determined. The conformations of the two molecules are different from each other but are similar to those found in the crystal structures of the homodisubstituted derivatives with which they are isomorphous p-bromo-N-(p-bromo-benzylidene) aniline (BrBr) and the orthorhombic form of p-chloro-N-(p-chloro-benzylidene)aniline (ClCl) respectively. Because of this isomorphous relationship it is concluded that the substituent on the benzylidene ring plays a crucial role in determining the packing mode of the structure.