Intermolecular C-F...H-C contacts in the molecular packing of three isostructural...

Among the three compounds reported here, namely N-(4-fluorophenyl)-β-D-mannopyranosylamine, (I), N-(3-fluorophenyl)-β-D-mannopyranosylamine, (II), and N-(2-fluorophenyl)-β-D-mannopyranosylamine, (III), all with chemical formula C(12)H(16)FNO(5), (I) and (II) are isostructural, whereas (III) assumes the same packing arrangement as the unfluorinated analogue N-phenyl-β-D-mannopyranosylamine, (IV), which has been reported previously. Similarities with respect to the intermolecular hydrogen-bonding patterns exist across the series (I)-(III). A packing motif that distinguishes the shared packing arrangement of (I) and (II) from that of (III) is a C-F...H-C chain of graph set C(4) that is preserved in the formal exchange of F and H atoms at the 4- and 3-positions on the aromatic ring of (I) and (II), but is replaced by a different chain of graph set C(5) when the F atom is located at the 2-position of the aromatic ring in (III). The steric role of the F atom in (I)-(III) is ambiguous but is examined here in detail.