**1. Introduction**

Phenolic compounds are a diverse class of bioactive secondary metabolites and are of high and significant importance [1–7]. They can be described as compounds that contain a phenol moiety. Phenol itself is a benzene ring that is substituted with a hydroxyl group (**Figure 1**). Thus, its systematic name is hydroxybenzene.

Phenolic compounds display a wide range of biological activities. For instance, they are known to exhibit antioxidants, antimicrobial, and anti-inflammatory properties. They are ubiquitous in nature. For instance, they are present in various types of fruits such as apple, banana, orange, mango, peach, papaya, strawberry, pomegranate, watermelon, and pineapple. For example, myricetin (a flavonol) is

*Phenolic Compounds - Chemistry, Synthesis, Diversity, Non-Conventional Industrial...*

**Figure 1.** *The structure of phenol.*

found in apple, gallic acid (a hydroxybenzoic acid) is found in banana, quercetin (a flavonol) and cyanidin (an anthocyanin) are found in pomegranate, *p*-coumaric acid (a hydroxycinnamic acid) and naringenin (a flavanone) are found in orange, vanilic acid (a hydroxybenzoic acid) and resveratrol (a stilbene) are found in strawberry, ferulic acid (a hydroxycinnamic acid) and apigenin (a flavone) are found in mango, and luteolin (a flavone) is found in watermelon and pineapple [8]. The health benefits of phenolic compounds are immense. Since original research articles and reviews on phenolic compounds are numerous in the literature, this chapter is not intended to be a comprehensive review of phenolic compounds. It is rather an attempt to complement existing article and reviews and to serve as a brief reference on their classification, analysis, chemistry, and synthesis.
