*3.1.1 Monoterpenes*

Carbides are almost always present. They are acyclic, monocyclic, or bicyclic. They sometimes constitute more than 90% of the essential oil (**Figure 7**).

*Phytochemistry, Medicinal Uses, and Beneficial Nutritional Effects of Essential Oils DOI: http://dx.doi.org/10.5772/intechopen.112696*

#### **Figure 7.**

*Acyclic (myrcene) and monocyclic (thymol) monoterpene [3].*

### *3.1.2 Sesquiterpenes*

They consist of 3 isoprene units. Chain elongation increases the number of possible cyclizations (**Figure 8**).

## *3.1.3 Other terpenoids*

These subgroups contain more than three isoprene units. They are presented as follows:


#### **3.2 Aromatic compounds**

Phenylpropane derivatives (C6–C3) are much less common than the previous ones. Very frequently, these are allyl and propenylphenols, sometimes aldehydes, characteristics of certain essential oils, such as that of clove (eugenol). On the other hand, the safarole is a compound with the chemical formula C6-C1 has been rarely identified in essential oils composition [24].

#### **3.3 Compounds of various origins**

Depending on their mode of extraction, essential oils can contain various aliphatic compounds, generally of low molecular mass, which can be carried away during

**Figure 8.** *Sesquiterpene (β-besabolene) [3].* hydrodistillation, such as carbide, acid (C3 to C10), alcohols, aldehydes (octanal, decanal), esters, lactones, nitrogen, or sulfur products [25].
