Ethylene glycol, Ethanediol, Dihydroxyethane
Propylene glycol, Propanediol, Dihydroxypropane
Butylene glycol, Butanediol, Dihydroxybutane
Ethylene glycol is common in automotive antifreeze mixtures. Because of its toxicity, it is sometimes replaced by propylene glycol, which is FDA approved for use in food, and is considered "generally accepted as safe". Ethylene glycol has a sweet taste, and accidental poisoning in children is a danger.
Propylene glycol and butylene glycol are often used as humectants (moisturizers) as they are hygroscopic (they draw moisture from the air).
Propylene glycol is what is used in artificial smoke or fog machines. It is also used as a preservative.
ethylene glycol: InChI=1/C2H6O2/c3-1-2-4/h3-4H,1-2H2
propylene glycol: InChI=1/C3H8O2/c1-3(5)2-4/h3-5H,2H2,1H3
butylene glycol: InChI=1/C4H10O2/c1-4(6)2-3-5/h4-6H,2-3H2,1H3