1. Volatile oil

2. Volatile oils different from fixed – secreted in oil cells in specialised structures ducts, gland, cell or glandular hairs – frequently associated with other substances gums, resins (resinify on exposure to air) mainly terpenoid – some phenol ethers and phenols

3. Terpenoids – based on the 5C isoprene unit – Monoterpenes most important, most volatile – di-, tri-, sesquiterpenes also important contain 2 condensed 5C units head-tail

4. Monoterpene components Hydrocarbons Alcohols

5. Aldehydes – all produced via the terpenoid pathway Ketones Citral

6. Esters Oxides

7. Sesquiterpenes (C 15 ) Hydrocarbons Phenols Phenolic esters Anethole

8. Chemical and physical properties volatile liquids with no colour – keep in amber bottles with minimum air odour asymetric centres, isomers with optical activity – only one isomer occurs naturally refractive index normally high – is a means to characterise the oil miscible in water and soluble in organic solvents – more soluble if contains –OH fatty acids reasonably heat stable – can be steam distilled tend to be used as solvents for resins

9. Families Economically only a few family groups are commercially useful [1] Labiatae Lavender, Mentha Sp. oil occurs in special organs – synthesized in glandular trichomes (mint) [2] Umbelliferae Fruits (best if ripe): anise, caraway, fennel, coriander found in “vittae” in the outer layer is characteristic

10. [3] Pinaceae Pine, juniper found in resin ducts in outer old xylem or bark released when bark removed [4] Rutaceae Citrus fruits typical ductless sacs in outer part of fruit – rind less stable, need more care [5] Lauraceae Cinnamon, camphor from region immediately below bark

11. Uses as inhalations, orally, gargles, mouthwashes, trans-dermally [1] Flavours & carminatives [2] Local stimulants and antiseptics (containing phenols) [3] Perfumes [4] Insect repellant, antimating device [5] Starting materials