Phenols, sometimes called phenolics, are a class of chemical compounds consisting of a hydroxyl functional group (-OH) attached to an aromatic hydrocarbon group. The simplest of the class is phenol (C₆H₅OH). Although similar to alcohols, phenols have unique properties including relatively higher acidities due to the aromatic ring tightly coupling with the oxygen and a relatively loose bond between the oxygen and hydrogen. The acidity of the hydroxyl group in phenols is commonly intermediate between aliphatic alcohols and carboxylic acids. Loss of a positive hydrogen from the hydroxyl group of a phenol forms a negative phenolate ion.

Some phenols are germicidal and are used in formulating disinfectants. Others possess estrogenic or endocrine disrupting activity.

Phenolic compounds

• Phenol, the parent compound, used as an disinfectant and for chemical synthesis.
• Salicylic acid, a plant hormone and analgesic, antipyretic, and anti-inflammatory drug, precursor compound to Aspirine.
• Propofol, a short-acting intravenous anesthetic agent.
• Cannabinoids, the active constituents of Cannabis.
• Psilocin, a hallucinogenic alkaloid of Psilocybe mushrooms.
• Capsaicin, the pungent compound of chilli peppers.
• Tyrosine, an amino acid.
• The neurotransmitters serotonin, dopamine, adrenaline, and noradrenaline.
• L-DOPA, a drug to treat Parkinson's disease.
• Eugenol, the main constituent of the essential oil of clove.
• Chavibetol from betel.
• Estradiol and other estrogens.
• Diethylstilbestrol, a synthetic estrogen with a stilbene structure.
• Methyl salicylate, the major constituent of the essental oil of wintergreen.
• Guaiacol (2-methoxyphenol) from roasted coffee, whisky, and smoke that has a smokey flavor.
• Raspberry ketone a compound with an intense raspberry smell.
• Gallic acid, found in gallnuts .
• Polyphenols like the flavonoids and tannins.
• Orthophenyl phenol , a fungicide used for waxing citrus fruits.
• Picric acid, an explosive material.
• The pH indicators phenolphthalein, phenol red, bromothymol blue, thymolphthalein, and bromophenol blue.
• 4-Nonylphenol , a breakdown product of detergents and nonoxynol-9.
• Thymol (2-Isopropyl-5-methyl phenol), an antiseptic that is used in mouthwashes.
• Cresols from coal tar and creosote.
• BHT (butylated hydroxytoluene), a fat-soluble antioxidant and food additive.
• ... and many more.