3,3′-Difluoro-4,4′-(p-phenylenedioxy)dibenzonitrile

The title compound, C20H10F2N2O2, was synthesized from hydroquinone and 3,4-difluorobenzonitrile. The centroid of the central aromatic ring is on a crystallographic center of inversion. The dihedral angle between the central and terminal rings is 77.8 (3)°. In the crystal, chains linked by C—H⋯N bond occur.

The title compound, C 20 H 10 F 2 N 2 O 2 , was synthesized from hydroquinone and 3,4-difluorobenzonitrile. The centroid of the central aromatic ring is on a crystallographic center of inversion. The dihedral angle between the central and terminal rings is 77.8 (3) . In the crystal, chains linked by C-HÁ Á ÁN bond occur.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: IM2138).

Comment
There has been growing interest in the study of hydroquinone derivatives which are important intermediates in the synthesis of herbicides (Liu, 2002. Bao et al., 2007. Only a few compounds of this kind have been structurally characterized so far.
As part of our studies, we have synthesized the title compound from hydroquinone and 3,4-difluorobenzonitrile and report it's crystal structure in this article.
The crystal structure of the title compound ( Fig. 1) utilizes the symmetry of the crystallographic inversion center similarily to a related selenium compound (Sørensen et al., 2009). The two terminal (C1-C7) phenyl ring and the central ring together with the attached oxygen (C8-C10/O1) form three planes. Due to crystallograhic symmetry the two terminal phenyl rings are coplanar. The terminal (C1-C7) phenyl ring plane and the central ring plane enclose a dihedral angle of 77.8 (3)°.
In the crystal structure, intermolecular C-H···N hydrogen bonds (Tab.1) connect neighboring molecules with each other to form a one-dimensional chain that stretches along the c axis (Fig.2).

Experimental
A DMF (10 ml) solution of hydroquinone (1 mmol) and 3,4-difluorobenzonitrile (2 mmol) was heated to 70°C in the presence of KOH and stirred for 37 h. Then the mixture was washed with water (30 ml) and extracted with ethyl acetate (three times).
The organic solvent was removed under reduced pressure. Afterwards the product was purified by column chromatography on silica (pentane -ethyl acetate mixtures). Single crystals were obtained by slow evaporation of the solvent of an ethanolic solution at room temperature.

Refinement
H atoms were placed in calculated positions with C-H=0.93 Å. All H atoms were included in the final cycles of refinement using a riding model, with U iso (H)=1.2U eq of the carrier atoms.   Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.