Phthalic acid, also known as o-phthalic acid or 1,2-benzenedicarboxylic acid, is an aromatic dicarboxylic acid with the chemical formula C₈H₆O₄. It is a white, crystalline solid that is not important industrially. It is formed as a byproduct in the manufacture of phthalic anhydride.

Methacrylic acid, also known as α-methylacrylic acid or 2-methylpropenoic acid, is an organic acid with the formula CH2=C(CH3)COOH. It is a colorless, moderately volatile, corrosive liquid with a strongly acrid odor.

Salicylic acid, also known as 2-hydroxybenzoic acid or o-hydroxybenzoic acid, is an aromatic compound with the formula C7H6O3. It is a colorless, odorless, crystalline solid that is found naturally in many plants, primarily as esters.

Tartaric acid, also known as acidum tartaricum, 2,3-dihydroxybutanedioic acid (IUPAC nomenclature), is a white crystalline organic acid found naturally in many fruits with the formula C4H6O6. The molecule possesses two asymmetric carbon centers with two carboxylic acid groups and a dialcohol in the same molecule, resulting in four stereoisomers.

Lactic acid, also known as 2-hydroxypropionic acid, is a natural organic acid with the molecular formula CH3CH(OH)COOH. Pure lactic acid is a white, crystalline solid with a low melting point that is found in many biological systems, including the human body.

Crotonic acid is the trans-isomer of 2-butenoic acid. It is a short-chain, unsaturated carboxylic acid with the chemical formula CH3CH=CHCOOH. The cis isomer of 2-butenoic acid is known as isocrotonic acid.