*2.2.1 Benzene ring*

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

**225**

**Table 1.**

*Phenolic Compounds*

*DOI: http://dx.doi.org/10.5772/intechopen.96740*

replacement of atoms [9, 10].

*2.2.2 Phenolic hydroxyl group*

**Structure Class**

C15 Flavans C15 Flavones C15 Flavanones C15 Flavanonols C15 Anthocyanidine C15 Anthocyanine C30 Biflavonyls

C6, C10, C14 Quinones C18 Betacyanine Lignans, neolignans Dimers or oligomers

Lignin Polymers

Phlobanhenea Polymers

*Classification of phenolic compounds.*

Tannins oligomers or polymers

C6-C1 simple phenolics

C6-C2 phenolic acids and related compounds C6-C3 acetophenones and phenylacetic acids

C15 coumarins, isocoumarins, and chromones C15 chalcones, aurones, dihydrochalcones

C6- C1- C6, C6- C2- C6 benzophenones, xanthones, &\$\$\$;tilbenes

C6-C3 cinnamic acids, cinnamyl aldehydes, cinnamyl alcohols

more acidic [8–10].

**2.3 Classification**

(**Table 1**) [9].

to delocalization of the π-electrons is very much favorable and also have tendency to refurbishing aromaticity. Aromatic compounds do not easily undergo any addition reactions and a double bond is replaced by two single bonds, as we see in regular alkenes i.e., linear chains of carbon atoms containing at least one double bond. Aromatic compounds show a partially replaced the reactions, that means the

It depends upon the chemical properties of the benzene with a hydroxyl group ring and the foremost property is acidity which are generally weak acids. As compared to hydroxyl group of unsubstituted aliphatic alcohols, phenolic OH-group is

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.

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

**Figure 1.** *Phenol.*

#### *Phenolic Compounds DOI: http://dx.doi.org/10.5772/intechopen.96740*

to delocalization of the π-electrons is very much favorable and also have tendency to refurbishing aromaticity. Aromatic compounds do not easily undergo any addition reactions and a double bond is replaced by two single bonds, as we see in regular alkenes i.e., linear chains of carbon atoms containing at least one double bond. Aromatic compounds show a partially replaced the reactions, that means the replacement of atoms [9, 10].
