fenoles

Fenoles, or phenols, are a class of aromatic compounds that contain one or more hydroxyl (-OH) groups attached directly to an aromatic ring. The simplest member is phenol (C6H5OH). The hydroxyl substituent imparts acidity and enables extensive hydrogen bonding, distinguishing phenols from many other alcohols.

Phenols are weak acids; for phenol, the pKa is about 10 in water, meaning partial deprotonation forms the phenoxide anion. The negative charge is delocalized over the aromatic ring by resonance, stabilizing the conjugate base. Substituents on the ring modulate acidity: electron-withdrawing groups increase acidity, electron-donating groups decrease it. Phenols can form phenolate salts with bases, increasing water solubility.

Classification and examples: Monophenols include phenol, o-/m-/p-cresol; dihydroxybenzenes such as catechol (1,2-dihydroxybenzene), resorcinol (1,3-dihydroxybenzene), and hydroquinone (1,4-dihydroxybenzene). More complex polyphenols occur in nature and in polymers. Many phenols are industrially important, for example in phenolic resins, antioxidants, and as precursors to polymers and dyes; bisphenol A is a widely known example.

Reactions and chemistry: The hydroxyl group activates the ring for electrophilic aromatic substitution at ortho and para positions relative to the OH group. In basic media, phenols are converted to phenoxide salts that act as nucleophiles in alkylation and acylation to form ethers and esters. Oxidation yields quinones; oxidation state changes underpin some dye and pigment chemistry.

Safety and environment: Phenols range from relatively modest irritants to highly toxic caustics. They require careful handling to avoid skin contact and inhalation, and can be hazardous to aquatic systems.