Diethyl [hydroxy(phenyl)methyl]phosphonate

Molecules of the title compound, C11H17O4P, are linked into chiral helical chains along the crystallographic b axis via O—H⋯O hydrogen bonds between the hydroxy group and an O atom of the phosphonate group. One ethyl group is disordered over two positions; the site occupancy factors are ca 0.7 and 0.3.

Molecules of the title compound, C 11 H 17 O 4 P, are linked into chiral helical chains along the crystallographic b axis via O-HÁ Á ÁO hydrogen bonds between the hydroxy group and an O atom of the phosphonate group. One ethyl group is disordered over two positions; the site occupancy factors are ca 0.7 and 0.3.
In I, the C10 and C11 atoms are disordered over two sets of sites with occupancies of 0.727 (7) and 0.273 (7). All bond distances and bond angles of I are normal and call for no further comment.
Molecules of I are linked into chiral helical chains by this H-bonding, running parallel to the b axis (Fig. 2). But these chains are aligned in an antiparallel fashion to form inversion centers in the crystal, thus the whole structure is achiral (Fig.3).

Experimental
All chemicals were obtained from commercial sources and used directly without further purification. Magnesium oxide (2 g) was added to a stirred mixture of diethyl phosphite (0.02 mol) and aldehyde (0.02 mol) at room temperature. After 2 h the mixture was washed by dichloromethane (50 ml) and dried with CaCl 2 ; evaporation of the solvent gave the crude product.

Refinement
All H atoms were positioned geometrically and were allowed to ride on their parent atoms, with C-H distances of 0.93-0.97Å (0.82Å for O-H group) and U iso (H) values constrained to be 1.2 (1.5 for -OH and -CH 3 group) times U eq of the carrier atom. Fig. 1. A molecular structure of I with the atom numbering scheme. Displacement ellipsoids are drawn at 30% probability level. Only major part of disoprdered moiety are presented. The H atoms are drawn as a small spheres of arbitrary radius.

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