any of the hydrocarbons with the general formula C₁₅H₂₄ (trimers of isoprene) or oxygen derivatives of these hydrocarbons. The name “sesquiterpenes” indicates that the molecular weight of these compounds is 1.5 times greater than that of the monoterpenes (from the Latin sesqui, “one and one-half times”). Sesquiterpenes, like terpenes, occur in essential oils and balsams and account for the characteristic odors of plants.