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

The title compound, C(16)H(26)NO(2) (+)·C(7)H(5)O(2) (−), 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.