Regular Monoterpenes and Sesquiterpenes Essential Oils

Institute of Animal Nutrition and Functional Plant Compunds, University of Veterinary Medicine 

Terpenoids represent a large class of natural products with numerous biological functions. Although terpenoids are usually regarded as secondary (plant) products, some of them are widespread and are involved in basic biological processes as electron transport in mitochondria and plastides. The name terpenoids is derived from turpentine, the aromatic resinlike exudations obtained from various coniferous trees. The common feature of all terpenoids is that they are built up by branched C5 units, isoprene (= 2-methylbutadiene). Terpenoids derived from just one isoprene unit are called hemiterpenes. 

Iridoids are monoterpenoids with a cyclopentane fused to a tetrahydropyran ring. In secoiridoids, the cyclopentane ring is opened. Most of these compounds are nonvolatile glycosides and will be reviewed elsewhere. 

This chapter has its main focus on mono- and sesquiterpenes as volatile compounds in essential oils. Since the mid of the 1990 as reliable and easy to operate 

Essential oils are complex mixtures of volatile constituents isolated from the plant material by hydrodistillation or steam distillation or expression in the case of citrus fruits. Extracts with apolar solvents yielding also the apolar terpenoids should not be designated as essential oils. Besides mono- and sesquiterpenes, essential oils may contain nonterpenoid hydrocarbons, phenylpropanoids, esters, lactones, phthalides, nitrogen- or sulfur-containing constituents, and isothiocyanates [5]. 

---