text: A diol is a chemical compound containing two hydroxyl groups (−OH groups). This pairing of functional groups is pervasive, and many subcategories have been identified. They are used as protecting groups of carbonyl groups, making them essential in synthesis of organic chemistry.
  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−(CH)−OH and propylene-1,3-diol, or beta propylene glycol, HO−CH−CH−CH−OH.