N-[4-(4-Nitrophenoxy)phenyl]propionamide

The title compound, C15H14N2O4, is an important intermediate for the synthesis of thermotropic liquid crystals. The dihedral angle between the two aromatic rings is 84.29 (4)°. An N—H⋯O hydrogen bond connects the molecules into chains running along the b axis. In addition, the crystal packing is stabilized by weak C—H⋯O hydrogen bonds.


Comment
Liquid crystals are materials which exhibit phases where molecular order is intermediate between that of an ordered solid and a disordered liquid. They represent the combined properties of both the crystalline state (e.g. optical and electrical anisotropy) and the liquid state (e.g. molecular mobility and fluidity). The two major classes of liquid crystals are thermotropic and lyotropic, which can be distinguished by the mechanism that drive their self-organization. Background information on liquid crystals and their various applications were surveyed, for example, by Collings (1990), Bahadur (1992), and Collings & Hird (1997. One of the basic characteristics for the establishment of the mesophase is the ratio of rigid and flexible portions in the main structure (Cârlescu et al., 2005). Therefore such type of precursors can be used to study structure property relationship of the liquid crystalline materials.
The crystal structure of the compound reported here is an important intermediate for the synthesis of thermotropic liquid crystals (Akhter et al., 2007).
In the molecule of the title compound ( Fig. 1), the bond lengths (Allen et al., 1995) and angles are within normal ranges.
The dihedral angle between the two aromatic rings is 84.29 (4)°. An N-H···O hydrogen bond connects the molecules to chains running along the b axis. In addition, the crystal packing is stabilized by weak C-H···O hydrogen bonds.

Experimental
A mixture of 5.046 g (50 mmol) 4-aminophenol, 6.91 g (50 mmol) anhydrous K 2 CO 3 and 5.3 ml (50 mmol) 4-nitrofluorobenzene in 70 ml DMF was heated at 373 K for 18 h in an inert atmosphere. After cooling to room temperature, the reaction mixture was poured into 800 ml of water to yield a yellow solid. The product was filtered, dried and then re-crystallized from nhexane (yield 86%). In a second step, propanoic acid and thionylchloride were refluxed in equimolar amounts for 30 min before evaporating excessive thionylchloride with a vacuum pump. The above prepared 4-[4-nitrophenoxy]aniline was then added to the propanoyl chloride solution in dry THF. 1 ml of triethylamine was also added for 1 g of 4-[4-nitrophenoxy]aniline and refluxed for 2 h under inert conditions. The reaction mixture was allowed to stand at room temperature overnight and filtered off the salt formed. The filterate was evaporated using a rotary evaporator, and the crude product obtained was re-crystallized from toluene (yield 76%, m.p. 416 K).

Refinement
All H atoms could be located from difference Fourier maps. Except the amino H atom that was freely refined, all other H atoms were refined using a riding model with U iso (H) = 1.2U eq (C) and U iso (H) = 1.5U eq (C methyl ) and distance restraints of