6-Cyanonaphthalen-2-yl 4-hexylbenzoate

In the title compound, C24H23NO2, a whole molecule is disordered over two sets of sites with occupancies in a ratio of 0.692 (6):0.308 (6). In the major disorder component, the naphthalene ring system forms a dihedral angle of 68.6 (5)° with the benzene ring. The corresponding angle in the minor component is 81.6 (10)°. In the crystal, molecules are linked into chains propagating along the b-axis direction via weak C—H⋯O hydrogen bonds. The crystal packing is further consolidated by weak C—H⋯π interactions.

In the title compound, C 24 H 23 NO 2 , a whole molecule is disordered over two sets of sites with occupancies in a ratio of 0.692 (6):0.308 (6). In the major disorder component, the naphthalene ring system forms a dihedral angle of 68.6 (5) with the benzene ring. The corresponding angle in the minor component is 81.6 (10) . In the crystal, molecules are linked into chains propagating along the b-axis direction via weak C-HÁ Á ÁO hydrogen bonds. The crystal packing is further consolidated by weak C-HÁ Á Á interactions.  Table 1 Hydrogen-bond geometry (Å , ).

Comment
Electro-optical display devices require certain desirable features such as large positive dielectric anisotropy, nematic phase, low melting point, stability and lack of color (Cox & Clecak, 1976;Reddy & Tschierske, 2006;Hanasaki et al., 2011). To obtain such properties, a highly polar terminal cyano group can be incorporated to give a large dipole moment.
Maximum dipole moment (90 degrees) indicates that the dipole moment is exactly parallel to the molecular short axis, which acts along the long axis of the molecule and helps to give the proper alignment for liquid crystal displays (Coates & Gray, 1976;Klingbiel et al., 1974;Takezoe & Takanishi, 2006). Here we report the synthesis and single-crystal X-ray study of an unsymmetrical naphthalene liquid crystal molecule. The shows a nematic phase after 379 K then a stable phase until an isotropic state at 411 K on a heating cycle. Upon cooling from the isotropic state, the nematic phase was reformed at 410 K, the phase is stabilized before crystallizes at 321 K.
The molecular structure of the title compound is shown in Fig 1. The whole molecule of the title compound is disordered over two positions with a refined site-occupancy ratio of 0.692 (6): 0.308 (6). For the major component, the naphthalene ring system (C2A-C11A) makes a dihedral angle of 68.6 (5)° with the benzene ring (C13A-C18A). In the minor component, the dihedral angle formed between the naphthalene ring system (C2B-C11B) and the benzene ring (C13B-C18B) is 81.6 (10)°. All the bond lengths (Allen et al., 1987) and angles are in normal ranges and compared with the closely related structures (Kuzmina et al., 2010;Blake et al., 1995;Li, 2006) In the crystal, molecules are linked into chains propagating along the b-axis via weak C-H···O hydrogen bonds. Weak C-H···π interactions are also observed (see Table 1).

Experimental
A mixture of 4-hexylbenzoic acid (1.0 mmol), 2-cyano-6-hydroxy-naphthalene (1.0 mmol), dicyclohexylcarbodiimide (1.2 mmol) and catalytic quantity of N,N-dimethylaminopyridine in 5 ml of dry dichloromethane was stirred at room temperature for 1 h. Progress of the reaction was monitored by TLC (ethyl acetate: pet ether 2:8). After completion of the reaction, the reaction mass was diluted with water and extracted into dichloromethane (25 ml). The organic layer was washed with diluted acetic acid and water. The organic layer was dried over anhydrous sodium sulfate and the solvent was removed under reduced pressure. The crude product was purified by column chromatography by using ethyl acetate: petroleum ether (2:8) as eluent and the product was recrystallization from chloroform. Yield = 70% as colourless block

Refinement
The title compound is disordered over two positions with a refined site-occupancy ratio of 0.692 (6): 0.308 (6) and the minor disordered component was refined isotropically. All H atoms were positioned geometrically [C-H = 0.95-0.99 Å] and refined using a riding model with U iso (H) = 1.2 or 1.5 U eq (C). A rotating group model was applied to the methyl groups. The restraints of same geometries were applied to all disordered components. Identical anisotropic displacement and distance restraint were used in the final refinement. Similarity were applied to the disordered atoms. DFIX restraints of 1.50 (1) Å were used for the long-disordered alkyl chains such as C19B-C20B, C21B-C22B, C22B-C23B, C23B -C24B and C23A-C24A distances. Same U ij parameters restraints were used for C22A/C23A and C22B/C23B atom pairs. One outlier (1 1 10) was omitted from the reflection data.

Figure 1
The molecular structure of the title compound showing 30% probability displacement ellipsoids for the major component of disorder. Open bonds show the minor disordered component.

Figure 2
The crystal packing of the title compound. Dashed lines represent the intermolecular hydrogen bonds. Only major disordered component is shown.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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 R-factors(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
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