Dextromethorphan is the dextrorotatory enantiomer of levomethorphan, which is the methyl ether of levorphanol, both opioid analgesics. It is named according to IUPAC rules as (+)-3-methoxy-17-methyl-9α,13α,14α-morphinan. As its pure form, dextromethorphan occurs as an odorless, opalescent white powder. It is freely soluble in chloroform and insoluble in water; the hydrobromide salt is water-soluble up to 1.5 g/100 mL at 25 °C. Dextromethorphan is commonly available as the monohydrated hydrobromide salt, and is also available in extended-release formulations (sold as dextromethorphan polistirex) contain dextromethorphan bound to an ion-exchange resin based on polystyrene sulfonic acid. Dextromethorphan's specific rotation in water is +27.6° (20 °C, Sodium D-line).