In the closely related quinoline compounds 8-nitro-2-(trichloromethyl)quinoline, (I), 6-nitro-2-(trichloromethyl)quinoline, (II), and 5-nitro-2-(trichloromethyl)quinoline, (III), all C(10)H(5)Cl(3)N(2)O(2), which are of both reactivity and pharmacological interest, and for which the biological activity and cytotoxicity appear to be based on the positions of the CCl(3) and nitro substituents, the nitro group is only coplanar with its aromatic substrate in (II). The deviation of the nitro group from coplanarity is concluded to be a function of both its position with respect to the trichloromethyl group and the intermolecular contacts in which it participates. The discrepancies between the crystal structures and the molecular shapes predicted by ab initio calculations are also explained in these terms. The quinoline ring is not rigorously planar in any of the structures, which may be explained by stress produced by the CCl(3) substituent.