Structure of N,4-dinitroaniline and its complex with sulfolane at 85 K; on the proton donor-acceptor affinity of the primary nitramine (HNNO2) group.

Abstract

The NNO2 group of the title compound is significantly less twisted with respect to the aromatic ring in comparison to a typical secondary nitramine. The amide nitrogen is trigonally hybridized. The nitramino group is almost planar. The C-C-N-N torsion angles vary between ca 13 and 42 degrees, whereas the twist along the N-N bond is much smaller and amounts to between ca 1 and 15 degrees. Those twist angles are governed by a crystal packing and are much larger in the case of crystals of pure N,4-dinitroaniline in comparison to that of its complex with sulfolane. The deviations of the internal angles of the aromatic ring from 120 degrees do not exceed 3 degrees. The presence of the nitro group increases the C-C-C valence angle of ca 2.0-2.6 degrees, whereas an analogous effect associated with the nitramino group is much smaller (ca 0.3-1.3 degrees), pointing to its weak electron-withdrawing properties. The nitramino group displays no tendency to conjugate with an electron-demanding substituent across the ring. It participates in hydrogen bonding only as a hydrogen-bonding donor. It does not act as a proton acceptor, despite the fact that nitramine rearrangement is catalysed by acids.