A diol is a chemical compound containing two hydroxyl groups (−OH groups).[1] An aliphatic diol may also be called a glycol.[2] 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.[3]
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−(CH2)4−OH and propylene-1,3-diol, or beta propylene glycol, HO−CH2−CH2−CH2−OH.