What does diol mean?
In chemistry, a diol is an organic compound that carries two hydroxyl (-OH) groups, making it a dihydric alcohol. The two hydroxyl groups may sit on adjacent carbon atoms — in which case the compound is called a vicinal diol — or elsewhere in the same molecule. Diols occupy a central place in industrial and laboratory chemistry: ethylene glycol, the simplest and best-known example, serves both as automobile antifreeze and as a raw material for polyester fibres such as polyethylene terephthalate. Because their twin hydroxyl groups can each react independently, diols are versatile building blocks, appearing in polymer synthesis, solvents, cosmetics, and pharmaceutical intermediates. The word is formed from the Greek-derived prefix "di-", meaning two, combined with the chemical suffix "-ol" denoting an alcohol. Though essential vocabulary within chemistry, "diol" remains almost entirely confined to technical contexts and is seldom encountered in general prose.
nounA chemical compound containing two hydroxyl (-OH) groups, typically on different carbon atoms of the same molecule; a dihydric alcohol.
- A dihydric alcohol: an organic compound bearing two hydroxyl (-OH) groups.
"Ethylene glycol is the simplest diol and is widely used as an antifreeze agent."
"The chemist reduced the ketone to form a vicinal diol in a single step."
"Polyester manufacture commonly relies on reacting a diol with a dicarboxylic acid."
Regular English plural; standard in scientific writing when referring to members of this class of compounds.
"Vicinal diols can be cleaved by periodic acid to yield carbonyl compounds."
The antifreeze in your car's radiator is a diol — ethylene glycol, the simplest member of a family defined purely by carrying two -OH groups.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of diol
The word "diol" is a transparent chemical coinage combining the prefix "di-", from Greek "dis" meaning "twice" or "double", with the suffix "-ol", the standard ending introduced by chemists to denote alcohols. It arose in nineteenth-century organic chemistry as systematic nomenclature developed for classifying compounds by the number of hydroxyl groups they contain. Its formation parallels other prefixed alcohol names such as "triol" for compounds with three hydroxyl groups.
How diol is actually used
Strictly a technical term used in organic and polymer chemistry; it rarely appears outside scientific writing. "Glycol" is the more familiar everyday term, especially for ethylene glycol.
Easily confused with diol
"Dial" is a face or control marked for measurement (or a verb meaning to phone), whereas "diol" is strictly a chemistry term for a compound with two hydroxyl groups.