6-[(4′-Ethoxycarbonyl-[1,1′-biphenyl]-4-yl)oxy]hexanoic acid

In the title compound, C21H24O5, the dihedral angle between the benzene rings is 19.57 (15)°. In the crystal, the molecular arrangement makes up head-to-head centrosymmetric dimers assembled by pairs of O—H⋯O bonds; this arrangement builds a graph-set ring motif of R 2 2(8). The dimers are linked into a tape running along the b-axis direction through C—H⋯O interactions. The packing is further consolidated by C—H⋯π interactions, forming layers parallel to (10-2).

In the title compound, C 21 H 24 O 5 , the dihedral angle between the benzene rings is 19.57 (15) . In the crystal, the molecular arrangement makes up head-to-head centrosymmetric dimers assembled by pairs of O-HÁ Á ÁO bonds; this arrangement builds a graph-set ring motif of R 2 2 (8). The dimers are linked into a tape running along the b-axis direction through C-HÁ Á ÁO interactions. The packing is further consolidated by C-HÁ Á Á interactions, forming layers parallel to (102).

Comment
Hydrogen bonds are the strongest of the non-covalent interactions and have a high degree of directionality. Therefore, the design of molecules with hydrogen bonding capabilities is very important due to its numerous potential application (Braga et al., 2004) in nanotechnology, in crystal engineering, in template synthesis of polymers and networks, as well as in templated processes in biology such as the replication and transcription of nucleic acids. It has long been known that monocarboxylic acid may be interlinked to form the cyclic hydrogen-bonded dimer. This kind of molecular dimer, is well known as supramolecular synthon in crystals of carboxylic acids (Jeong et al., 2006;Leiserowitz et al., 1976). It is also important to point out that the title compound I contains a polymerizable end-group. Therefore it is a precursor for polymeric materials.
In the title compound, the ASU shows a molecule with two non-coplanar phenyl rings bonded by C10 and C13, both rings with p-substitution. The dihedral angle between these planes is 19.57 (15)°. On the other hand, C2 to C6 show an aliphatic extended-chain probably due to intermolecular interactions. The crystal packing makes up a head to head dimer assembled by intermolecular O-H···O bonds between the carboxyl groups ( Fig. 1). This arrangement builds a graph-set ring R 2 2 (8) (Etter et al., 1990;Bernstein et al., 1995). Two more interactions C-H···O and C-H···π interactions, are identified, which stabilize the crystal packing. A tape of molecules from the C18-H18···O1 interaction is formed along the b axis. The C6-H6A···Cg1 interaction is building a layer of molecules parallel to (1 0 2). (Table 1; Cg1 is the centroid of the ring composed of C13-C18.)

Experimental
6.2 g (14 mmol) of benzyl 6-(ethyl 4′-oxydiphenyl-4-carboxylate)-hexanoate was added to 90 ml of dry ethyl acetate. 5% Pd-C (0.029 g) was then added with stirring. The hydrogenolisis was allowed to proceed for 8.5 h under hydrogen atmosphere at room temperature. After the removal of the catalyst by filtration and evaporation of the ethyl acetate under reduced pressure, the residue was then dissolved in hot methylene chloride and the solution was allowed to cool to -10 °C. It gave a white crystalline solid which was filtered off (4.8 g, 13.48 mmol, yield 97%

Refinement
H atoms linked to C and O atoms were placed in geometrical idealized positions (C-H = 0.93-0.97 Å and O-H = 0.82 Å) and refined as riding on their parent atoms, with U iso (H) = 1.2 U eq (C) or 1.5 U eq (C methyl , O).

Figure 1
A view of the centrosymmetric dimer of the title compound. Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
A crystal packing view of the title compound. Displacement ellipsoids are drawn at the 50% probability level.