Role of intermolecular interactions involving organic fluorine in trifluoromethylated benzanilides

Abstract

Trifluoromethylated benzanilides, containing C(sp³)–F bonds, have been synthesized and their crystal and molecular structures have been investigated to highlight the significance of weak intermolecular interactions associated with the presence of organic fluorine in a molecule. It is observed that the molecular conformation and packing characteristics are a delicate interplay amongst different intermolecular interactions, namely strong N–H⋯OC, weak C–H⋯OC, C–H⋯F–C, and C–H⋯π H-bonds, along with C–F⋯F–C and C–F⋯π intermolecular interactions in the solid state. All the isomers are associated with variations in crystal packing due to the presence of different supramolecular variants introduced by the presence of a trifluoromethyl group at the ortho, meta and para positions of the phenyl ring. Furthermore, a comparison of the experimental molecular conformation with that obtained from DFT theoretical calculations delineates the significant role of the trifluoromethyl group on the phenyl ring, which results in variations in conformational flexibility associated with the molecule. It has been observed that the –CF₃group is associated with rotational disorder in some of the crystalline solids and the overall crystal structure is stabilized by a network of C(sp²)–H⋯F–C(sp³) intermolecular H-bonds and C–(sp³)F⋯F–C(sp³) contacts [the “fluorous effect”] in the crystalline lattice. It is also observed that there also exists a definite relationship between the acidity of the participating hydrogens with the hydrogen bonding characteristics of such weak C–H⋯F–C H-bonds in the crystal.