(9H-Fluoren-9-yl)(phen-yl)phosphinic acid.

The crystal structure of the title compound, C19H15O2P, features pairs of mol-ecules joined by O-H⋯O hydrogen bonds across crystallographic inversion centers. In addition, π-π inter-actions, with a centroid-centroid distance of 3.6273 (9) Å between the fluorene ring systems, connect the dimers into chains along [01-1].

rac-Eth-yl(phen-yl)phosphinic acid.

The crystal structure of the title compound, C8H11O2P, features O-H⋯O hydrogen bonds, which link mol-ecules related by the b-glide plane into chains along [010].

Meth-yl(phen-yl)phosphinic acid.

The crystal structure of the title compound, C(7)H(9)O(2)P, displays O-H⋯O hydrogen bonding , which links individual mol-ecules related via the c-glide plane and translational symmetry along the crystallographic b-axis direction into continuous chains.

Benz-yl(phen-yl)phosphinic acid.

The title compound, C(13)H(13)O(2)P, crystallized as enanti-omerically pure crystals; for the crystal measured, the P atom has R stereochemistry. The crystal structure displays O-H⋯O hydrogen bonding, which links individual mol-ecules related by a 2(1) screw axis parallel to the crystallographic a-axis direction into continuous chains.