The crystal structures of three benzanilide derivatives, which are oligomers of fire resistant polymers, are reported. The compound (I) is monoclinic, P21c, with a = 12.430(2), b = 13.535(2), c = 7.948(2) Å, β = 108.18(3)°; compound (II) is orthorhombic, P212121, with a = 25.236(2), b = 9.019(2), c = 5.639(1) Å, compound (III) is monoclinic, P21/a, with a = 23.622(3), b = 9.581(2), c = 10.373(2) Å, β = 99.08(3)°. The three structures have been solved by direct methods and refined to R = 0.042 for 1740, to R = 0.049 for 1200 and to R = 0.050 for 3811 observed reflections for compounds (I), (II) and (III) respectively.
Any molecule consists of four nearly planar parts: the ring of the benzoic acid, the amido group, the benzene ring methylated or not and the carboxylic group. Their reciprocal orientations, different in the three derivatives, is mainly due to the steric hindrance. Strong hydrogen bonds form dimers in compound (I) and infinite chains in compounds (II) and (III).
Energy calculations have been carried out in order to discuss the different packings and their influence on the molecules of investigated compounds.
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