Diethyl (1-hydroxy-1,2-diphenylethyl)phosphonate

In the title compound, C18H23O4P, the dihedral angle between the aromatic ring planes is 69.94 (14)°. Both ethyl side chains are disordered over two sets of sites, with occupancy ratios of 80:20 and 70:30. In the crystal, inversion dimers linked by pairs of O—H⋯O hydrogen bonds occur, leading to R 2 1(8) loops, and C—H⋯O and weak C—H⋯π interactions are also seen.

In the title compound, C 18 H 23 O 4 P, the dihedral angle between the aromatic ring planes is 69.94 (14) . Both ethyl side chains are disordered over two sets of sites, with occupancy ratios of 80:20 and 70:30. In the crystal, inversion dimers linked by pairs of O-HÁ Á ÁO hydrogen bonds occur, leading to R 2 1 (8) loops, and C-HÁ Á ÁO and weak C-HÁ Á Á interactions are also seen.

Comment
We have reported the preparation and crystal structures of the phosphonate compounds (Acar et al., 2009;Tahir et al., 2007Tahir et al., , 2009aTahir et al., , 2009b. In continuation to the study of phosphonate compounds, we, herein report the preparation and crystal structure of the title compound (I), (Fig. 1).
The crystal structures of (II) Dimethyl (1-hydroxy-1,2-diphenylethyl)phosphonate (Acar et al., 2009) has been reported which differs from (I) due to dimethylphosphonate instead of diethylphosphonate. In the title compound ethyl moieties of diethylphosphonate are disordered over two sites with occupancy ratios of 80:20 and 70:30, respectively. The disorder in diethyl moieties is also present in the reported structure (Tahir et al., 2009a). The present compound is basically dimerized forming ring motifs R 2 2 (10) (Bernstein et al., 1995) due to O-H···O type of intermolecular H-bonding (Fig. 2). The title molecule is also stabilized due to intermolecular H-bonding of C-H···O type and C-H···CgA interaction (Table 1), Where CgA is the centroid of the aromatic ring A (C9-C14). Ring motifs of R 2 1 (8) are also present which are formed due to the intermolecular H-bondings (Fig. 2). The dihedral angle between the ring A and the benzene ring B (C1-C6) is 69.94 (14)°.

Experimental
The title compound was prepared according to method described by Texier-Boullet & Lequitte (1986). In a solution mixture of 2-phenylacetophenone (3.92 g, 20 mmol) and diethylphosphonate (2.76 g, 20 mmol), a mixture of KF (5 g, 86.20 mmol) and commercial Al 2 O 3 (5 g, 49 mmol) was slowly added at 273 K. The reaction mixture remained at room temperature for two days. The product was extracted twice with CH 3 Cl 2 . The extracted product was recrystallized in a mixture of distalled water and ethyl alcohol to yield colourless prisms of (I).

Refinement
The coordinates of H-atom of hydroxy group were refined. C-bound H atoms were positioned geometrically, with C-H = 0.93, 0.96 and 0.97 Å for aromatic, methyl and ethylene moieties and constrained to ride on their parent atoms, with U iso (H) = xU eq (C, O), where x = 1.5 for methyl H, and x = 1.2 for all other H atoms.

Special details
Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles 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.