Conformational and solid-state studies of diphenyl 1-hydroxy-1-phenylethylphosphonate

The crystal structure of the title compound, diphenyl 1-hydroxy-1-phenylethylphosphonate (1), was determined by the single-crystal X-ray diffraction method. The crystallographic data for 1 are as follow: C₂₀H₁₉O₄P, Mr = 354.34, monoclinic, P₂₁/n, a = 9.787(1) Å, b = 20.235(1) Å, c = 9.797(1) Å, β= 106.18(3)°, V = 1863.3(4) ų, Z = 4, D_calc = 1.26 g/ cm³, λ(Mo-Ka) = 0.71073 Å, μ = 1.6cm^-1, F(000) = 744, R = 0.018, and R_w = 0.032 for 2258 observed reflections. The solid-state structure in a dimeric packing mode exhibits intermolecular hydrogen bonding of the type P=O ⋯ H-O. Infrared solution studies (CC1₄) indicate that upon high dilution (10^-4 M) the dimers completely dissociate to give conformers with and without intramolecular hydrogen bonds. Theoretical studies (PM3) were undertaken to determine the energy profile about the P-C torsional angle, which exhibited low energy barriers to rotation with no clear minimum energy conformation.