2-(2-Acetylamino-5-chlorophenyl)-2,2-difluoroethanoic acid and 2-(2-acetylamino-5-methylphenyl)-2,2-difluoroethanoic acid, and 2-(2-acetylaminophenyl)-2,2-difluoro-N-phenylacetamide and 2-(2-acetylaminophenyl)-N-(4-chlorophenyl)-2,2-difluoroacetamide: examples of variation in molecular packing and hydrogen-bonding motif induced by substituent change.

Among the title compounds, viz. the acids C10H8ClF2NO3, (I), and C11H11F2NO3, (II), and the amides C14H14F2N2O2, (III), and C14H13ClF2N2O2, (IV), the change of substituent from Cl in (I) to methyl in (II) has a dramatic effect upon the hydrogen bonding between the molecules, which occur in layers in both cases. In the structures of (III) and (IV), hydrogen bonds connect the molecules to form chains, but the introduction of a chloro substituent in (IV) has a profound effect on the orientation of the molecules within the chains and the packing of the chains in the structure as a whole.