. . "A diol is a chemical compound containing two hydroxyl groups (\u2014OH groups). This pairing of functional groups is pervasive and many subcategories have been identified. The most common industrial diol is ethylene glycol. Examples of diols in which the hydroxyl functional groups are more widely separated include 1,4-butanediol HO\u2014(CH2)4\u2014OH and bisphenol A, and propylene-1,3-diol or beta propylene glycol, HO-CH2-CH2-CH2-OH."@en .