Structural motifs in acetoacetanilides: the effect of a fluorine substituent

The structures of three fluoro-substituted acetoacetanilides, namely 2'-, 3'- and 4'-fluoroacetoacetanilide, all C(10)H(10)FNO(2), are presented and discussed. We observe a planar structure with intramolecular hydrogen bonding when the F atom is in the ortho position of the aromatic ring, and a twisted structure with intermolecular hydrogen bonding when the F atom is in the meta or para positions. It can be predicted which of these two structural motifs will be adopted by considering the position of any aromatic substituents. In this regard, fluorine appears to mimic the steric effect of a larger substituent, which we attribute to its high electronegativity.