Crystal and Molecular Structures of Acetoacetanilide, and o- and p-Chloroacetoacetanilides: X-Ray Crystallographic and MO Study

X-Ray structure analyses and MO calculations have been performed for acetoacetanilide (AAA), and o- and p-chloroacetoacetanilides (o-CAAA and p-CAAA) in order to elucidate the contribution of hydrogen bonding to crystal and molecular structures. The molecular conformations have been classified into two categories, planar for o-CAAA and nonplanar for AAA and p-CAAA. The molecular conformation of o-CAAA can be well-reproduced by the geometry optimization based on the AM1 (Austin Model 1) MO method, while those of AAA and p-CAAA are different from the optimized geometries. The deviation from the optimized structure can be explained on the basis of the formation of intermolecular hydrogen bonding and C–H···O=C interactions in the crystals. The hydrogen bonding of these compounds is discussed together with the infrared (IR) spectral data.