Phenylpropanoids are a large class of plant-derived secondary metabolites characterized by a phenyl ring attached to a three-carbon propanoid side chain. They include compounds such as cinnamic acid, eugenol, and ferulic acid, playing key roles in plant defense, lignin biosynthesis, and flavor/aroma in spices and foods. These compounds exhibit diverse bioactivities including antioxidant, antimicrobial, and anti-inflammatory properties. Their structures vary widely from simple acids to complex polymers like lignin. Solubility and physical properties differ significantly across members of the class, precluding single-value assignments for many parameters.