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|Section2= |Section7= |Section8= }} Menthol is an organic compound made synthetically or obtained from corn mint, peppermint or other mint oils. It is a waxy, crystalline substance, clear or white in color, which is solid at room temperature and melts slightly above. The main form of menthol occurring in nature is (−)-menthol, which is assigned the (1''R'',2''S'',5''R'') configuration. Menthol has local anesthetic and counterirritant qualities, and it is widely used to relieve minor throat irritation. Menthol also acts as a weak kappa opioid receptor agonist. ==Structure== Natural menthol exists as one pure stereoisomer, nearly always the (1''R'',2''S'',5''R'') form (bottom left corner of the diagram below). The eight possible stereoisomers are: In the natural compound, the isopropyl group is in the ''trans'' orientation to both the methyl and hydroxyl groups. Thus, it can be drawn in any of the ways shown: The (+)- and (–)-enantiomers of menthol are the most stable among these based on their cyclohexane conformations. With the ring itself in a chair conformation, all three bulky groups can orient in equatorial positions. The two crystal forms for racemic menthol have melting points of 28 °C and 38 °C. Pure (−)-menthol has four crystal forms, of which the most stable is the α form, the familiar broad needles. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「menthol」の詳細全文を読む スポンサード リンク
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