Crystal structure of {[2-hydroxy-2-(3-methoxyphenyl)cyclohexyl]methyl}dimethylammonium benzoate

The title compound, C16H26NO2 +·C7H5O2-, is a benzoate salt of the painkiller Tramadol. The six-membered cyclohexane ring of the cation adopts a slightly distorted chair conformation and carries OH and 3-methoxyphenyl substituents at the 2-position and a protonated methylazaniumylmethyl group at the 3-position. In addition, a weak intramolecular C - H⋯O hydrogen bond is observed in the cation. In the crystal, weak O - H⋯O, N - H⋯O and C - H⋯O hydrogen bonds link the components into chains along [010]. A C - H⋯π contact is also observed.