Whereas halothane (no longer commercially available) is an alkane, all of the other volatile anesthetics are ether derivatives. Isoflurane, enflurane, and desflurane are methyl ethyl ether derivatives, and sevoflurane is a methyl isopropyl ether. Isoflurane and enflurane are isomers, and desflurane differs from isoflurane in the substitution of a fluorine for a chlorine atom.