Crystal structure of (1R,2S,5R)-2-isopropyl-5-methyl-cyclohexanol (-)-menthol

In spite of the fact that menthol is commonly known and widely used in conf ectionery, cosmetics, medicine and pharmacy its crystal structure has not b een determined and published. The reason might be its high vapour pressure that makes the crystal handling difficult. Crystals sublimate in a few minu tes in open air at room temperature. The investigated sample crystal was ex tracted from the plant Mentha arvensis Linner. The essential oil of the pla nt was steam distilled and esterified to menthyl acetate. Menthol crystals were obtained after hydrolysis. Single crystal X-ray diffraction measuremen t was carried out at low temperature (143 K) using MoKalpha radiation. Qual itative optical rotation measurement proves the (-) or (1R,2S,5R) absolute configuration, one of the eight possible optically active stereoisomers. (- )-Menthol crystallises in the trigonal crystal system, space group P3(1), w ith three independent molecules in the asymmetric unit. Each molecule gener ates an infinite column of hydrogen bonded molecules related by the 3(1) sc rew axis.