phenol , Any of a class of organic compounds with a hydroxyl group (−OH; see functional group) attached to a carbon atom in a ring of an aromatic compound. The simplest one, carbolic acid (C6H5OH), is also called phenol; its most important reaction is with formaldehyde, with which it forms widely used polymers called phenol-formaldehyde (phenolic) resins. Phenols are similar to alcohols but form stronger hydrogen bonds (see bonding), so they dissolve more readily in water and boil at higher temperatures. They may be colourless liquids or white solids; many have a sharp, spicy odour. Some are found in essential oils. Phenols with higher molecular weights and phenol derivatives have supplanted phenol itself as industrial antiseptics (germicidal cleaners). See also Leo Baekeland.