**2.3 Classification**

*Bioactive Compounds - Biosynthesis, Characterization and Applications*

and sensory characteristics [8, 9].

**2.1 Definition**

phenol (**Figure 1**).

till now [8].

*2.2.1 Benzene ring*

and polyphenolic compounds; (2) terpenoids, and (3) nitrogen-containing alkaloids and sulfur-containing compounds. These compounds are linked to primary metabolite by biosynthetic enzymes and building blocks [8]. Phenolic compounds (flavonoids, allied phenolic, and polyphenolic compounds) are one among the secondary metabolites more cosmopolitan in plants. The shikimate, pentose phosphate and phenylpropanoid pathways are extract from plants. These compounds perform an important role in the growth and reproduction of plants, giving protection against pathogens and predators. In vegetables and fruits, PC contribute to color

**2. Phenolic compounds: definition, chemical properties, classification, biosynthesis, extraction technologies and medical importance**

The compounds that have one or more hydroxyl groups connected straightway

In phenols, the hydroxyl group is linked to a chain of carbons which are alike to alcohols of aliphatic structures. Due to the existence of the aromatic ring, the phenolic hydroxyl group is affect. The hydrogen of the phenolic hydroxyl is unstable

Its structure consists of an aromatic ring that contain 1 or more hydroxyl substituents. It may be classified into simple phenolic molecule and extremely polymerized compounds. The PC occur naturally is associated with one or more phenolic groups when combine with mono- and polysaccharides. In addition, they also can be linked to esters and methyl esters. They have a wide range in structure diversity that occurs in nature. More than 8000 structures of phenolic compound are studied

The carbon's atomic number is 6, i.e. it has 6 electrons and 6 protons. Electrons are around the atom's nucleus in orbitals. The benzene ring is representing one of two mesmeric complex. The double arrow indicates, the two drawn structures and the true structure of the molecule lies in between. Hence, as the six C-C bonds of the ring are identical, with the π-electrons over the entire ring which is more accurate to use structure. The affects of reactivity of aromatic compounds is due

to the ring of an aromatic. The whole category is based on the arrangement of

caused by the aromatic ring, that build the phenols as a weak acid [10].

**2.2 Chemical properties of phenolic compounds**

**224**

**Figure 1.** *Phenol.*

The word phenolics includes a very wide group of chemical compound. They can be classified in many ways. Harborne and Simmonds (1964) classified these compound into groups depends upon the numeral of carbons in the molecule. (**Table 1**) [9].

An another classification represented by Swain and Bate-Smith (1962). They categorized the phenols as "common[typical]" and "less common [less typical]".


### **Table 1.**

*Classification of phenolic compounds.*

Ribéreau-Gayon (1972) classified the phenols into three origins which is as follows: [10].

1.It is widely distributed in all plants or in a specific plant.

2.It is less widely distributed to known in confined number of compounds.

3.Phenolic component exists as polymers.
