4-dimethylamino-beta-nitrostyrene and 4-dimethylamino-beta-ethyl-beta-nitrostyrene at 100 K.

The structures of 4-dimethylamino-beta-nitrostyrene (DANS), C10H12N2O2, and 4-dimethylamino-beta-ethyl-beta-nitrostyrene (DAENS), C12H16N2O2, have been solved at T=100 K. The structure solution for DANS was complicated by the presence of a static disorder, characterized by a misorientation of 17% of the molecules. The molecule of DANS is almost planar, indicating significant conjugation, with a push-pull effect through the styrene skeleton extending up to the terminal substituents and enhancing the dipole moment. As a consequence of this conjugation, the hexagonal ring displays a quinoidal character; the lengths of the C-N [1.3595 (15) A] and C-C [1.448 (2) A] bonds adjacent to the benzene ring are shorter than single bonds. The molecules are stacked in dimers with antiparallel dipoles. In contrast, the molecule of DAENS is not planar. The ethyl substituent pushes the nitropropene group out of the benzene plane, with a torsion angle of -21.9 (3). Nevertheless, the molecule remains conjugated, with a shortening of the same bonds as in DANS.