Terpenes- volatile unsaturated hydrocarbons usually found in plants- essential oils which in turn provide the aroma or "smell." 

Isoprene itself, a C5H8 gaseous hydrocarbon, is emitted by the leaves of various plants as a natural byproduct of plant metabolism. Next to methane it is the most common volatile organic compound found in the atmosphere. Plants are pretty smart- terpenes provide natural defense against bugs/pests

Classification of terpenes is made on the basis of the number of carbon atoms of which they are composed, terpenes and their associated terpenoids  are terpenes that have some rearrangement or oxidation to create assorted functional groups (alcohols, esters etc.).

The prefix which is present in the names, is based on the number of units by which the terpene molecule is built up. For example, the hermiterpenes belong to the half-terpenes with five carbon atoms (C5) and the word mono, in monoterpenes for the number one. Sesqui stands for 1.5, di for 2 and tri for 3. heir associated terpenoids (also known as isoprenoids) are terpenes that have some rearrangement or oxidation to create assorted functional groups (alcohols, esters etc.).

So now we know what terpenes are at least their make up chemically- how are they made? Are they metabolites?  Starting with the monoterpenes - what are some of the compounds and aromas. Next post I will discuss.