TERPENES

TERPENES. Under the general name T. are understood hydrocarbons of the empirical formula (C₅H₈)_n and accordingly they are divided into: 1) hemiterpenes, C₅H₈; 2) monoterpenes, C₁₀H₁₆; 3) sesquiterpenes, C₁₅H₂₄; 4) polyterpenes, (C₅H₈)_n. Hemiterpenes, compounds with an open carbon chain, possess two ethylene bonds, are easily formed from more complex T. (turpentine, rubber, etc.) during dry distillation and conversely revert to T. upon their polymerization; a typical example is isoprene CH₂ = C(CH₃)-CH=CH₂. Monoterpenes can be both natural, occurring in plants, and artificial, obtained by laboratory methods; in general, about 15-20 isomers are known. In medicine, representatives of T. (e.g. camphor, menthol, thymol) are used similarly to essential oils in capsules, ointments, plasters, liquids, oil solutions, sometimes per se.