Essential Oil
Definition and meaning of Essential Oil in chemistry.
An essential oil is a concentrated, volatile mixture of hydrophobic organic compounds, chiefly terpenes, terpenoids, and phenylpropanoids, extracted from plant material, most often by steam distillation or cold pressing.
In more detail
Despite the name, an essential oil is not a "true" oil in the lipid sense (a triglyceride of fatty acids); it is called "essential" because it carries the plant's characteristic scent, or essence. Its small, lipophilic molecules have relatively low molecular weight and weak intermolecular forces, giving them high vapor pressure so they evaporate readily and are largely insoluble in water. Their high volatility and characteristic fragrance make essential oils widely used in perfumery, flavoring, and aromatherapy, though many constituents can also cause skin sensitization or irritation.
Key facts
| Field | Organic Chemistry |
|---|---|
| Major components | Terpenes, terpenoids, phenylpropanoids |
| Extraction methods | Steam distillation, cold pressing, solvent extraction |
| Physical properties | Volatile, lipophilic, insoluble in water |
Peppermint essential oil, obtained by steam distillation of Mentha piperita leaves, consists largely of the monoterpenoid menthol, a monoterpene alcohol (roughly 30-50%), along with menthone and other related terpenoids.
Frequently asked questions
Is an essential oil a true oil, like olive oil?
No. True oils (fats) are triglycerides of fatty acids, while essential oils are volatile mixtures of terpenes and other volatile organic compounds that are chemically unrelated to lipids.
Why do essential oils evaporate so easily?
Their molecules are small, typically C10 monoterpenes or C15 sesquiterpenes, with relatively weak intermolecular forces, giving them high vapor pressure at room temperature.