Part 4: Terpene Hydrocarbons—Diterpenes

A diterepene is the combination of two monoterpene units, for a total of 20 carbons. Because of their high molecular weights, these molecules are difficult to extract by steam distillation, and when present, are found in essential oils in very low amounts. Structurally, these are the largest volatile aromatic compounds that can be collected under normal distillation conditions. Essential oil constituents typically have low molecular weights, which contributes to their high volatility. Molecules cannot be collected by steam distillation if they have a molecular mass above the low 300s. Should a molecule with a molecular mass above this amount be found in an essential oil, it would be a sign of improper extraction conditions or adulteration. They are rarely found in most essential oils. Diterpenes that may be found in essential oils include camphorene, cafestol, kahweol, cambrene, and taxideme.