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, M_r = 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 = 1.6 cm⁻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 (CCl₄) 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. © 1996 John Wiley & Sons, Inc.