A three-dimensional refinement of the crystal structure of 4-nitroaniline

The structure of 4-nitroaniline has been refined three-dimensionally with visually-estimated Cu Ka data. Positional and thermal parameters for the carbon, nitrogen, and oxygen atoms, and positional parameters for the hydrogen atoms, were obtained by least squares. The standard errors in bond lengths not involving hydrogen are 0.006-0.007 A; the corresponding errors in bond angles are about 0.4 . Intramolecular bond distances were corrected for the effects of thermal motion. These distances are discussed, and compared with those in related molecules. The molecular geometry supports the view that there is a small but significant contribution of a quinonoid resonance form to the structure of the molecule, although the amino group appears to interact with the aromatic ring to a greater extent than does the nitro group. The nitro group shows a pronounced torsional oscillation, the r.m.s, amplitude being about 14; this sort of motion seems to be characteristic of nitro groups in aromatic compounds.