The group of terpenoids is the grand group plant compound, are meanwhile 36,000 different structures known there. Despite the large differences in their structure, all terpenoids are originating from the molecule isopentenyl diphosphate (IPP), that from exists of five carbon atoms. Terpenoids are classified on the basis of the number of carbon atoms:
Hemiterpenoids (five carbon atoms, C5), monoterpenoids (C10), sesquiterpenoids (C15), diterpenoids (C20), triterpenoids (C30), tetraterpenoids (C40) and polyterpenoids (larger than C40).

Rubber is an example of a polyterpenoid (larger than C40). Carotenoids are part of the group of tetraterpenoids (for example B-carotene from carrots, and lycopene, the red dye in tomatoes). The group of triterpenoids (C30) belongs to the steroids (for example ergosterol).

The diterpenoids (C20) are also known as the gibberellins acids, of this, there are more than 100 known. The gibberellins acids function as growth regulators (plant hormones) that under others the stem growth, regulate seed maturation and blossoming.

Mono- and sesquiterpenoids we also find in the ethereal oil of a plant. These compounds fall on through their smell. They are to find in various parts of a plant. Mono- and sesquiterpenoids have often a biological function. An example of the function of mono- and sesquiterpenoids is that heat evaporates these compounds, through which they form a protective haze around the plant that keeps harmful insects, bacteria, and molds at a distance. But these volatile compounds can also serve to attract favorable insects for instance for pollination. Another example of a function is that a plant after it is attacked by an insect a number of quick compounds will make. A natural enemy of the insect "smells" these compounds and goes to the plant this take out this insect. In this example, these terpenoids function as a kind of "Call for help!" compound. The function of these terpenoids can differ rather per specific mono- or sesquiterpenoid.
Alpha-isomethylionone is a colorless to pale oily liquid, an isomer of Methyl Ionone, but its sweet orris-like scent is felt more attractive.
Thanks to a sweet floral rose-like odor with citrus notes, it is mainly used as a fragrance, masking, and insect repellant ingredient in skin and hair care applications.
Primarily used as a fragrance in skin and hair care applications, Geraniol exhibits numerous beneficial properties, including antimicrobial, anti-inflammatory, insect repellent, and antioxidant action.
Besides its pleasant scent and masking function, Limonene is valued for its astringent, tonic, and binding action, as well as it can be used as a solvent for insoluble ingredients and for controlling the viscosity of the formulation.