Comparison of the structural motifs of acetoacetanilides and related azo pigments

The structures of three methyl-substituted acetoacetanilides and of an azo pigment derived from one of them are presented and discussed together with a review of related known crystal structures. By considering the position o f any aromatic substituents it is possible to predict whether the simple ac etoacetanilides adopt planar structures with intramolecular hydrogen bondin g or twisted structures featuring intermolecular hydrogen bonding. However, we rnd that the same crystal engineering rules cannot be applied to the re lated azo pigments: this is apparently due to the presence of an sp(2) atom which facilitates the adoption of planar conformations. The thermal proper ties of the acetoacetanilides were measured by DSC and are discussed with r eference to their crystal structures.